Vai al contenuto

sed command

sed: Stream Editor

Working principle: The sed command will read the currently processed row and place it in the "pattern space" for processing. After processing, the result will be output and the "pattern space" will be cleared. Next, read the next line and place it in the "pattern space" for processing, and so on, until the last line. Some documents also mention a term called "hold space" (also known as "temporary-storage space"), which can temporarily store some processed data and output it through "pattern space".

"pattern space" and "hold space": An area of memory where data is processed and stored.

For information not covered, review the sed manual.

The usage of the command is:

sed [OPTION]... {script-only-if-no-other-script} [input-file]...
options description
-n Output text lines that will only be processed by the sed command to the screen
-e Apply multiple sed operation commands to the input text line data
-f Call and execute sed script command file
-i Modify the original file
-r Regular expression
Operation command
(sometimes called operation instruction)		 description
s/regexp/replacement/ Replacement string
p Print the current "pattern space". Often used with the -n option, for example: cat -n /etc/services \| sed -n '3,5p'
d Delete "pattern space". Start next cycle
D Delete the first line of the "pattern space" and start next cycle
= Print Line Number
a \text Add one or more lines of content after the matching line. When adding multiple lines, all lines except the last line need to use "\" to indicate that the content has not ended
i \text Add one or more lines of content before the matching line. When adding multiple lines, all lines except the last line need to use "\" to indicate that the content is not ended
c \text Replace matching lines with new text
q Immediately exit the sed script
r Append text read from file
: label Label for b and t commands
b label Branch to label; if label is omitted, branch to end of script
t label If "s///" is a successful replacement, then jump to the label
h H Copy/append "pattern space" to "hold space"
g G Copy/append "hold space" to "pattern space"
x Exchange the contents of the hold and pattern spaces
l List out the current line in a "visually unambiguous" form
n N Read/append the next line of input into the "pattern space"
w FILENAME Write the current pattern space to FILENAME
! negation
& Referencing a string that already matches
Addresses description
first~step Use "first" to specify the first line, and 'step' to specify the step size. For example, outputting odd lines of text with sed -n "1~2p" /etc/services
$ Match the last line of text
/regexp/ Using regular expressions to match text lines
number Specify line number
addr1,addr2 Use line number positioning to match all lines from "addr1" to "addr2"
addr1,+N Use line number positioning to match addr1 and the N lines following addr1

Examples of usage

  1. Match and print (p)

    • Print a line that begins with a netbios string
    Shell > cat /etc/services | sed -n '/^netbios/p'
netbios-ns      137/tcp                         # NETBIOS Name Service
netbios-ns      137/udp
netbios-dgm     138/tcp                         # NETBIOS Datagram Service
netbios-dgm     138/udp
netbios-ssn     139/tcp                         # NETBIOS session service
netbios-ssn     139/udp

    Tip

    As we all know, double and single quotation marks in a shell play different roles. The $, `, and \ in double quotes have a special meaning. The recommendation is to use single quotes more often when using the sed command.

    • Print the text from lines 23 to 26
    Shell > cat -n /etc/services | sed -n '23,26p'
23  tcpmux          1/tcp                           # TCP port service multiplexer
24  tcpmux          1/udp                           # TCP port service multiplexer
25  rje             5/tcp                           # Remote Job Entry
26  rje             5/udp                           # Remote Job Entry
    • Print odd lines
    Shell > cat -n /etc/services | sed -n '1~2p'
1  # /etc/services:
3  #
5  # IANA services version: last updated 2016-07-08
7  # Note that it is presently the policy of IANA to assign a single well-known
9  # even if the protocol doesn't support UDP operations.
11  # are included, only the more common ones.
13  # The latest IANA port assignments can be gotten from
15  # The Well Known Ports are those from 0 through 1023.
17  # The Dynamic and/or Private Ports are those from 49152 through 65535
19  # Each line describes one service, and is of the form:
...
    • Print line 10 to the last line
    Shell > cat -n /etc/services | sed -n '10,$p'
10  # Updated from RFC 1700, ``Assigned Numbers'' (October 1994).  Not all ports
11  # are included, only the more common ones.
12  #
13  # The latest IANA port assignments can be gotten from
14  #       http://www.iana.org/assignments/port-numbers
15  # The Well Known Ports are those from 0 through 1023.
16  # The Registered Ports are those from 1024 through 49151
17  # The Dynamic and/or Private Ports are those from 49152 through 65535
...
    • Lines 10 to the last do not print
    Shell > cat -n /etc/services | sed -n '10,$!p'
1  # /etc/services:
2  # $Id: services,v 1.49 2017/08/18 12:43:23 ovasik Exp $
3  #
4  # Network services, Internet style
5  # IANA services version: last updated 2016-07-08
6  #
7  # Note that it is presently the policy of IANA to assign a single well-known
8  # port number for both TCP and UDP; hence, most entries here have two entries
9  # even if the protocol doesn't support UDP operations.
    • Print the line number and content of the matched string
    Shell > sed -n -e '/netbios/=' -e '/netbios/p' /etc/services
123
netbios-ns      137/tcp                         # NETBIOS Name Service
124
netbios-ns      137/udp
125
netbios-dgm     138/tcp                         # NETBIOS Datagram Service
126
netbios-dgm     138/udp
127
netbios-ssn     139/tcp                         # NETBIOS session service
128
netbios-ssn     139/udp
    • Match string range and print it

    Use commas to separate string ranges

    Shell > cat  /etc/services | sed -n '/^netbios/,/^imap/p'
netbios-ns      137/tcp                         # NETBIOS Name Service
netbios-ns      137/udp
netbios-dgm     138/tcp                         # NETBIOS Datagram Service
netbios-dgm     138/udp
netbios-ssn     139/tcp                         # NETBIOS session service
netbios-ssn     139/udp
imap            143/tcp         imap2           # Interim Mail Access Proto v2

    Info

    Start of range: Match the line where the string is located, only matching the first string that appears. End of range: Match the line where the string is located, only matching the first string that appears.

    Shell > grep -n ^netbios /etc/services
123:netbios-ns      137/tcp                         # NETBIOS Name Service
124:netbios-ns      137/udp
125:netbios-dgm     138/tcp                         # NETBIOS Datagram Service
126:netbios-dgm     138/udp
127:netbios-ssn     139/tcp                         # NETBIOS session service
128:netbios-ssn     139/udp

Shell > grep -n ^imap /etc/services
129:imap            143/tcp         imap2           # Interim Mail Access Proto v2
130:imap            143/udp         imap2
168:imap3           220/tcp                         # Interactive Mail Access
169:imap3           220/udp                         # Protocol v3
260:imaps           993/tcp                         # IMAP over SSL
261:imaps           993/udp                         # IMAP over SSL

    In other words, the content printed above is lines 123 to 129

    • Print the line where the string is located and until the last line
    Shell > cat /etc/services | sed -n '/^netbios/,$p'
    • Using variables in bash scripts
    Shell > vim test1.sh
#!/bin/bash
a=10

sed -n ''${a}',$!p' /etc/services
# or
sed -n "${a},\$!p" /etc/services
    • Regular expression

    Matches only "Three Digits" + "/udp".

    Shell > cat /etc/services | sed -r -n '/[^0-9]([1-9]{3}\/udp)/p'
sunrpc          111/udp         portmapper rpcbind      # RPC 4.0 portmapper UDP
auth            113/udp         authentication tap ident
sftp            115/udp
uucp-path       117/udp
nntp            119/udp         readnews untp   # USENET News Transfer Protocol
ntp             123/udp                         # Network Time Protocol
netbios-ns      137/udp
netbios-dgm     138/udp
netbios-ssn     139/udp
...

  2. Match and delete (d)

    It is similar to printing, except that the operation command is replaced with d and the -n option is not required.

    • Delete all lines that match the udp string, and delete all comment lines, and delete all Blank line
    Shell > sed -e '/udp/d' -e '/^#/d' -e '/^$/d' /etc/services
tcpmux          1/tcp                           # TCP port service multiplexer
rje             5/tcp                           # Remote Job Entry
echo            7/tcp
discard         9/tcp           sink null
systat          11/tcp          users
daytime         13/tcp
qotd            17/tcp          quote
chargen         19/tcp          ttytst source
ftp-data        20/tcp
ftp             21/tcp
ssh             22/tcp                          # The Secure Shell (SSH) Protocol
telnet          23/tcp
...
    • Delete consecutive lines of text
    Shell > cat -n /etc/services | sed '10,$d'
1  # /etc/services:
2  # $Id: services,v 1.49 2017/08/18 12:43:23 ovasik Exp $
3  #
4  # Network services, Internet style
5  # IANA services version: last updated 2016-07-08
6  #
7  # Note that it is presently the policy of IANA to assign a single well-known
8  # port number for both TCP and UDP; hence, most entries here have two entries
9  # even if the protocol doesn't support UDP operations.
    • Regular expression
    Shell > cat  /etc/services | sed -r '/(tcp)|(udp)|(^#)|(^$)/d'
http            80/sctp                         # HyperText Transfer Protocol
bgp             179/sctp
https           443/sctp                        # http protocol over TLS/SSL
h323hostcall    1720/sctp                       # H.323 Call Control
nfs             2049/sctp       nfsd shilp      # Network File System
rtmp            1/ddp                           # Routing Table Maintenance Protocol
nbp             2/ddp                           # Name Binding Protocol
echo            4/ddp                           # AppleTalk Echo Protocol
zip             6/ddp                           # Zone Information Protocol
discard         9/sctp                  # Discard
discard         9/dccp                  # Discard SC:DISC
...

  3. Replace strings(s///g)

    Syntax Syntax description
    sed 's/string/replace/g' FILENAME s: All lines representing the content of the file. You can also specify the range of lines, for example: sed '20,200s/netbios/TMP/g' /etc/services
    g (Global): If there is no g, This means that when multiple matching strings appear on a single line, only the first matching string will be replaced.
    /: Delimiter style. You can also specify other styles, for example: sed '20,200s?netbios?TMP?g' /etc/services

    Tip

    Example in the bash script:

    Shell > vim /root/sedReplace.sh
#!/bin/bash
a="SELINUX=enforcing"
b="SELINUX=disabled"

sed -i 's/'${a}'/'${b}'/g' /etc/selinux/config
# or
sed -i "s/${a}/${b}/g" /etc/selinux/config
    • Replace and print
    Shell > sed -n '44,45s/ssh/SSH/gp' /etc/services
SSH             22/tcp
SSH             22/udp
    • Use the "&" symbol to reference a string
    Shell > sed -n '44,45s/ssh/&-SSH/gp' /etc/services
ssh-SSH             22/tcp
ssh-SSH             22/udp
    • Use a string to locate one or more lines and replace the specified string within the line range
    Shell > grep ssh /etc/services -n
44:ssh             22/tcp                          # The Secure Shell (SSH) Protocol
45:ssh             22/udp                          # The Secure Shell (SSH) Protocol
551:x11-ssh-offset  6010/tcp                        # SSH X11 forwarding offset
593:ssh             22/sctp                 # SSH
1351:sshell          614/tcp                 # SSLshell
1352:sshell          614/udp                 #       SSLshell
1607:netconf-ssh     830/tcp                 # NETCONF over SSH
1608:netconf-ssh     830/udp                 # NETCONF over SSH
7178:sdo-ssh         3897/tcp                # Simple Distributed Objects over SSH
7179:sdo-ssh         3897/udp                # Simple Distributed Objects over SSH
7791:netconf-ch-ssh  4334/tcp                # NETCONF Call Home (SSH)
8473:snmpssh         5161/tcp                # SNMP over SSH Transport Model
8474:snmpssh-trap    5162/tcp                # SNMP Notification over SSH Transport Model
9126:tl1-ssh         6252/tcp                # TL1 over SSH
9127:tl1-ssh         6252/udp                # TL1 over SSH
10796:ssh-mgmt        17235/tcp               # SSH Tectia Manager
10797:ssh-mgmt        17235/udp               # SSH Tectia Manager

Shell > sed '/ssh/s/tcp/TCP/gp' -n  /etc/services
ssh             22/TCP                          # The Secure Shell (SSH) Protocol
x11-ssh-offset  6010/TCP                        # SSH X11 forwarding offset
sshell          614/TCP                 # SSLshell
netconf-ssh     830/TCP                 # NETCONF over SSH
sdo-ssh         3897/TCP                # Simple Distributed Objects over SSH
netconf-ch-ssh  4334/TCP                # NETCONF Call Home (SSH)
snmpssh         5161/TCP                # SNMP over SSH Transport Model
snmpssh-trap    5162/TCP                # SNMP Notification over SSH Transport Model
tl1-ssh         6252/TCP                # TL1 over SSH
ssh-mgmt        17235/TCP               # SSH Tectia Manager
    • String replacement for consecutive lines
    Shell > sed '10,30s/tcp/TCP/g' /etc/services
    • Multiple matches and replacements
    Shell > cat /etc/services | sed 's/netbios/test1/g ; s/^#//d ; s/dhcp/&t2/g'
    • Group replacement of regular expressions

    In regular expressions, a "()" is a grouping. \1 represents reference group 1, \2 represents reference group 2, and so on.

    Shell > cat /etc/services
...
axio-disc       35100/tcp               # Axiomatic discovery protocol
axio-disc       35100/udp               # Axiomatic discovery protocol
pmwebapi        44323/tcp               # Performance Co-Pilot client HTTP API
cloudcheck-ping 45514/udp               # ASSIA CloudCheck WiFi Management keepalive
cloudcheck      45514/tcp               # ASSIA CloudCheck WiFi Management System
spremotetablet  46998/tcp               # Capture handwritten signatures

Shell > cat /etc/services | sed -r 's/([0-9]*\/tcp)/\1\tCONTENT1/g ; s/([0-9]*\/udp)/\1\tADD2/g'
...
axio-disc       35100/tcp       CONTENT1               # Axiomatic discovery protocol
axio-disc       35100/udp       ADD2               # Axiomatic discovery protocol
pmwebapi        44323/tcp       CONTENT1               # Performance Co-Pilot client HTTP API
cloudcheck-ping 45514/udp       ADD2               # ASSIA CloudCheck WiFi Management keepalive
cloudcheck      45514/tcp       CONTENT1               # ASSIA CloudCheck WiFi Management System
spremotetablet  46998/tcp       CONTENT1               # Capture handwritten signatures

    \t: That is, a tab

    • Replace all comment lines with blank space
    Shell > cat /etc/services | sed -r 's/(^#.*)//g'
...
chargen         19/udp          ttytst source
ftp-data        20/tcp
ftp-data        20/udp

ftp             21/tcp
ftp             21/udp          fsp fspd
ssh             22/tcp                          # The Secure Shell (SSH) Protocol
ssh             22/udp                          # The Secure Shell (SSH) Protocol
...
    • Replace one of the lowercase letters of a word with a capital letter
    Shell > echo -e "hello,world\nPOSIX" | sed -r 's/(.*)w/\1W/g'
hello,World
POSIX
    • String position swapping
    Shell > cat /etc/services
...
cloudcheck-ping 45514/udp               # ASSIA CloudCheck WiFi Management keepalive
cloudcheck      45514/tcp               # ASSIA CloudCheck WiFi Management System
spremotetablet  46998/tcp               # Capture handwritten signatures

    We can divide this file into five parts:

    cloudcheck-ping    45514       /     udp        # ASSIA CloudCheck WiFi Management keepalive
 ↓                   ↓         ↓      ↓               ↓
(.*)           (\<[0-9]+\>)   \/   (tcp|udp)         (.*)
 ↓                   ↓                ↓               ↓ 
 \1                 \2               \3              \4

    Shell > cat /etc/services | sed -r 's/(.*)(\<[0-9]+\>)\/(tcp|udp)(.*)/\1\3\/\2\4/g'
...
edi_service     udp/34567               # dhanalakshmi.org EDI Service
axio-disc       tcp/35100               # Axiomatic discovery protocol
axio-disc       udp/35100               # Axiomatic discovery protocol
pmwebapi        tcp/44323               # Performance Co-Pilot client HTTP API
cloudcheck-ping udp/45514               # ASSIA CloudCheck WiFi Management keepalive
cloudcheck      tcp/45514               # ASSIA CloudCheck WiFi Management System
spremotetablet  tcp/46998               # Capture handwritten signatures
    • Remove any blank characters
    Shell > echo -e "abcd\t1 2 3 4\tWorld"
abcd    1 2 3 4 World
Shell > echo -e "abcd\t1 2 3 4\tWorld" | sed -r 's/(\s)*//g'
abcd1234World

  4. Execute multiple times using the -e option

    The following example:

    Shell > tail -n 10 /etc/services
aigairserver    21221/tcp               # Services for Air Server
ka-kdp          31016/udp               # Kollective Agent Kollective Delivery
ka-sddp         31016/tcp               # Kollective Agent Secure Distributed Delivery
edi_service     34567/udp               # dhanalakshmi.org EDI Service
axio-disc       35100/tcp               # Axiomatic discovery protocol
axio-disc       35100/udp               # Axiomatic discovery protocol
pmwebapi        44323/tcp               # Performance Co-Pilot client HTTP API
cloudcheck-ping 45514/udp               # ASSIA CloudCheck WiFi Management keepalive
cloudcheck      45514/tcp               # ASSIA CloudCheck WiFi Management System
spremotetablet  46998/tcp               # Capture handwritten signatures

Shell > tail -n 10 /etc/services | sed  -e '1,3d' -e '/cloud/s/ping/PING/g'
# or
Shell > tail -n 10 /etc/services | sed  '1,3d ; /cloud/s/ping/PING/g'      
edi_service     34567/udp               # dhanalakshmi.org EDI Service
axio-disc       35100/tcp               # Axiomatic discovery protocol
axio-disc       35100/udp               # Axiomatic discovery protocol
pmwebapi        44323/tcp               # Performance Co-Pilot client HTTP API
cloudcheck-PING 45514/udp               # ASSIA CloudCheck WiFi Management keepalive
cloudcheck      45514/tcp               # ASSIA CloudCheck WiFi Management System
spremotetablet  46998/tcp               # Capture handwritten signatures

  5. Add content above or below a specific line (i and a)

    • Add two lines of content above the specified line number
    Shell > tail -n 10 /etc/services > /root/test.txt
Shell > cat /root/test.txt
aigairserver    21221/tcp               # Services for Air Server
ka-kdp          31016/udp               # Kollective Agent Kollective Delivery
ka-sddp         31016/tcp               # Kollective Agent Secure Distributed Delivery
edi_service     34567/udp               # dhanalakshmi.org EDI Service
axio-disc       35100/tcp               # Axiomatic discovery protocol
axio-disc       35100/udp               # Axiomatic discovery protocol
pmwebapi        44323/tcp               # Performance Co-Pilot client HTTP API
cloudcheck-ping 45514/udp               # ASSIA CloudCheck WiFi Management keepalive
cloudcheck      45514/tcp               # ASSIA CloudCheck WiFi Management System
spremotetablet  46998/tcp               # Capture handwritten signatures

Shell > cat /root/test.txt | sed '3i 123\
abc'
aigairserver    21221/tcp               # Services for Air Server
ka-kdp          31016/udp               # Kollective Agent Kollective Delivery
123
abc
ka-sddp         31016/tcp               # Kollective Agent Secure Distributed Delivery
edi_service     34567/udp               # dhanalakshmi.org EDI Service
axio-disc       35100/tcp               # Axiomatic discovery protocol
axio-disc       35100/udp               # Axiomatic discovery protocol
pmwebapi        44323/tcp               # Performance Co-Pilot client HTTP API
cloudcheck-ping 45514/udp               # ASSIA CloudCheck WiFi Management keepalive
cloudcheck      45514/tcp               # ASSIA CloudCheck WiFi Management System
spremotetablet  46998/tcp               # Capture handwritten signatures
    • Add three lines below the specified line number
    Shell > cat /root/test.txt | sed '5a 123\
comment yes\
tcp or udp'
aigairserver    21221/tcp               # Services for Air Server
ka-kdp          31016/udp               # Kollective Agent Kollective Delivery
ka-sddp         31016/tcp               # Kollective Agent Secure Distributed Delivery
edi_service     34567/udp               # dhanalakshmi.org EDI Service
axio-disc       35100/tcp               # Axiomatic discovery protocol
123
comment yes
tcp or udp
axio-disc       35100/udp               # Axiomatic discovery protocol
pmwebapi        44323/tcp               # Performance Co-Pilot client HTTP API
cloudcheck-ping 45514/udp               # ASSIA CloudCheck WiFi Management keepalive
cloudcheck      45514/tcp               # ASSIA CloudCheck WiFi Management System
spremotetablet  46998/tcp               # Capture handwritten signatures
    • Match a specific line based on a string and add 2 lines of content above it
    Shell > cat /root/test.txt | sed '/tcp/iTCP\
UDP'
TCP
UDP
aigairserver    21221/tcp               # Services for Air Server
ka-kdp          31016/udp               # Kollective Agent Kollective Delivery
TCP
UDP
ka-sddp         31016/tcp               # Kollective Agent Secure Distributed Delivery
edi_service     34567/udp               # dhanalakshmi.org EDI Service
TCP
UDP
axio-disc       35100/tcp               # Axiomatic discovery protocol
axio-disc       35100/udp               # Axiomatic discovery protocol
TCP
UDP
pmwebapi        44323/tcp               # Performance Co-Pilot client HTTP API
cloudcheck-ping 45514/udp               # ASSIA CloudCheck WiFi Management keepalive
TCP
UDP
cloudcheck      45514/tcp               # ASSIA CloudCheck WiFi Management System
TCP
UDP
spremotetablet  46998/tcp               # Capture handwritten signatures

  6. Replace lines (c)

    • Locate one or more lines based on a string and replace these lines of text
    Shell > cat /root/test.txt | sed '/ser/c\TMP1 \
TMP2'
TMP1
TMP2
ka-kdp          31016/udp               # Kollective Agent Kollective Delivery
ka-sddp         31016/tcp               # Kollective Agent Secure Distributed Delivery
TMP1
TMP2
axio-disc       35100/tcp               # Axiomatic discovery protocol
axio-disc       35100/udp               # Axiomatic discovery protocol
pmwebapi        44323/tcp               # Performance Co-Pilot client HTTP API
cloudcheck-ping 45514/udp               # ASSIA CloudCheck WiFi Management keepalive
cloudcheck      45514/tcp               # ASSIA CloudCheck WiFi Management System
spremotetablet  46998/tcp               # Capture handwritten signatures
    • Single line replacement
    Shell > cat /root/test.txt | sed '7c REPLACE'
aigairserver    21221/tcp               # Services for Air Server
ka-kdp          31016/udp               # Kollective Agent Kollective Delivery
ka-sddp         31016/tcp               # Kollective Agent Secure Distributed Delivery
edi_service     34567/udp               # dhanalakshmi.org EDI Service
axio-disc       35100/tcp               # Axiomatic discovery protocol
axio-disc       35100/udp               # Axiomatic discovery protocol
REPLACE
cloudcheck-ping 45514/udp               # ASSIA CloudCheck WiFi Management keepalive
cloudcheck      45514/tcp               # ASSIA CloudCheck WiFi Management System
spremotetablet  46998/tcp               # Capture handwritten signatures
    • Replace consecutive lines of text
    Shell > cat /root/test.txt | sed '2,$c REPLACE1 \
replace2'
aigairserver    21221/tcp               # Services for Air Server
REPLACE1
replace2
    • Replace even numbered lines
    Shell > cat /root/test.txt | sed '2~2c replace'
aigairserver    21221/tcp               # Services for Air Server
replace
ka-sddp         31016/tcp               # Kollective Agent Secure Distributed Delivery
replace
axio-disc       35100/tcp               # Axiomatic discovery protocol
replace
pmwebapi        44323/tcp               # Performance Co-Pilot client HTTP API
replace
cloudcheck      45514/tcp               # ASSIA CloudCheck WiFi Management System
replace

  7. Read the contents of the file and append its contents below the matching line (r)

    Shell > cat /root/app.txt
append1
POSIX
UNIX

Shell > cat /root/test.txt | sed '/ping/r /root/app.txt'
aigairserver    21221/tcp               # Services for Air Server
ka-kdp          31016/udp               # Kollective Agent Kollective Delivery
ka-sddp         31016/tcp               # Kollective Agent Secure Distributed Delivery
edi_service     34567/udp               # dhanalakshmi.org EDI Service
axio-disc       35100/tcp               # Axiomatic discovery protocol
axio-disc       35100/udp               # Axiomatic discovery protocol
pmwebapi        44323/tcp               # Performance Co-Pilot client HTTP API
cloudcheck-ping 45514/udp               # ASSIA CloudCheck WiFi Management keepalive
append1
POSIX
UNIX
cloudcheck      45514/tcp               # ASSIA CloudCheck WiFi Management System
spremotetablet  46998/tcp               # Capture handwritten signatures

  8. Write matching lines to other files (w)

    Shell > cat /root/test.txt | sed '/axio/w /root/storage.txt'

Shell > cat /root/storage.txt
axio-disc       35100/tcp               # Axiomatic discovery protocol
axio-disc       35100/udp               # Axiomatic discovery protocol

  9. Read/append the next line of input into the "pattern space" (n and N)

    • Print the next line of the matching line
    Shell > cat /root/test.txt
aigairserver    21221/tcp               # Services for Air Server
ka-kdp          31016/udp               # Kollective Agent Kollective Delivery
ka-sddp         31016/tcp               # Kollective Agent Secure Distributed Delivery
edi_service     34567/udp               # dhanalakshmi.org EDI Service
axio-disc       35100/tcp               # Axiomatic discovery protocol
axio-disc       35100/udp               # Axiomatic discovery protocol
pmwebapi        44323/tcp               # Performance Co-Pilot client HTTP API
cloudcheck-ping 45514/udp               # ASSIA CloudCheck WiFi Management keepalive
cloudcheck      45514/tcp               # ASSIA CloudCheck WiFi Management System
spremotetablet  46998/tcp               # Capture handwritten signatures

Shell > cat /root/test.txt | sed '/ping/{n;p}' -n
cloudcheck      45514/tcp               # ASSIA CloudCheck WiFi Management System

    Tip

    Multiple sed operation commands may affect each other, and you can use "{ }" to reduce this effect.

    • Print even text lines

    First, read the first line, as an n command is present; the second line will be printed out, and so on.

    Shell > cat -n /root/test.txt | sed -n '{n;p}'
# or
Shell > cat -n /root/test.txt | sed -n '2~2p'
2  ka-kdp          31016/udp               # Kollective Agent Kollective Delivery
4  edi_service     34567/udp               # dhanalakshmi.org EDI Service
6  axio-disc       35100/udp               # Axiomatic discovery protocol
8  cloudcheck-ping 45514/udp               # ASSIA CloudCheck WiFi Management keepalive
10  spremotetablet  46998/tcp               # Capture handwritten signatures
    • Print odd text lines
    Shell > cat -n /root/test.txt | sed -n '{p;n}'
# or
Shell > cat -n /root/test.txt | sed -n '1~2p'
# or
Shell > cat -n /root/test.txt | sed 'n;d'
1  aigairserver    21221/tcp               # Services for Air Server
3  ka-sddp         31016/tcp               # Kollective Agent Secure Distributed Delivery
5  axio-disc       35100/tcp               # Axiomatic discovery protocol
7  pmwebapi        44323/tcp               # Performance Co-Pilot client HTTP API
9  cloudcheck      45514/tcp               # ASSIA CloudCheck WiFi Management System
    • Print 3n lines
    Shell > cat -n /root/test.txt | sed -n '{n;n;p}'
# or
Shell > cat -n /root/test.txt | sed -n '3~3p'
3  ka-sddp         31016/tcp               # Kollective Agent Secure Distributed Delivery
6  axio-disc       35100/udp               # Axiomatic discovery protocol
9  cloudcheck      45514/tcp               # ASSIA CloudCheck WiFi Management System
    • N

    Read the first line and append one line after encountering the N command. In this example, the "pattern space" is "1\n2". Finally, execute the q command to exit.

    Shell > seq 1 10 | sed 'N;q'
1
2

    Because there is no additional line after line 9, the output is as follows:

    Shell > seq 1 9 | sed -n 'N;p'
1
2
3
4
5
6
7
8

    When the last line is read, the N command is not executed and the output is as follows:

    Shell > seq 1 9 | sed -n '$!N;p'
1
2
3
4
5
6
7
8
9

    Merge two lines into one line. Replace the "\n" of the "pattern space" with a blank character.

    Shell > seq 1 6 | sed 'N;{s/\n//g}'
12
34
56

  10. Ignore case (I)

    There seems to be no information about ignoring case in man 1 sed.

    Shell > echo -e "abc\nAbc" | sed -n 's/a/X/Igp'
Xbc
XBC

    Shell > cat /etc/services | sed '/OEM/Ip' -n
oem-agent       3872/tcp                # OEM Agent
oem-agent       3872/udp                # OEM Agent
oemcacao-jmxmp  11172/tcp               # OEM cacao JMX-remoting access point
oemcacao-rmi    11174/tcp               # OEM cacao rmi registry access point
oemcacao-websvc 11175/tcp               # OEM cacao web service access point

    Shell > cat /etc/services | sed -r '/(TCP)|(UDP)/Id'

    Shell > cat /etc/services | sed -r '/(TCP)|(UDP)/Ic TMP'

  11. Gets the total number of lines in a file

    Shell > cat /etc/services | sed -n '$='
# or
Shell > cat /etc/services | wc -l

11473

Author: tianci li