Awk command (1)
1. Advantages and disadvantages of awk:
Advantages: 1.awk is used to fetch columns, and it is simple and convenient to fetch columns alone.
2.awk supports regular expressions
3.awk support variables
4.awk supports & & and | |
5.awk supports process control statements such as if and if/else conditional control
6.awk supports loops such as while, do-while, and for loops
7.awk supports commands for jump or exit, such as break, continue, next, exit, etc.
8.awk support function
Disadvantages: awk is powerful and relatively complex
Second, the command format of awk:
Awk 'condition 1 {Action 1} condition 2 {Action 2}. File.txt
Third, the usage of awk:
1. Print lines that match root
[root@localhost ~] # awk'/ root/' / etc/passwd
Root:x:0:0:root:/root:/bin/bash
Operator:x:11:0:operator:/root:/sbin/nologin
2. The role of the Mutual F option
2.1 separate with colons, print the first column of data; without the-F option, the default is a space, and colons can be customized.
[root@localhost] # awk-F:'{print $1 for 3, 5 for 7}'/ etc/passwd
Root 0 root / bin/bash
Bin 1 bin/ sbin/nologin
Daemon 2 daemon / sbin/nologin
...
2.2-F custom delimiter to separate data
[root@localhost] # df-h
Filesystem Size Used Avail Use% Mounted on
/ dev/mapper/VolGroup00-LogVol00
57G 7.2g 47G 14% /
/ dev/sda1 99m 12m 82m 13% / boot
Tmpfs 252m 0 252m 0% / dev/shm
[root@localhost ~] # df-h | grep / $| awk'{print $4}'| awk-F "%"'{print $1}'
fourteen
The 2.3cut command is also implemented
[root@localhost ~] # df-h | grep / $| awk'{print $4}'| cut-d "%"-f 1
fourteen
2.4 when printing columns, use commas to separate columns
[root@localhost ~] # awk-F:'/ root/ {print $1 $3 $5 $7}'/ etc/passwd
Root0root/bin/bash
Operator11operator/sbin/nologin
[root@localhost ~] # awk-F:'/ root/ {print $1, 3, 5, 5, 7}'/ etc/passwd
Root 0 root / bin/bash
Operator 11 operator / sbin/nologin
2.5 when printing columns, # to separate columns
[root@localhost ~] # awk-F:'/ root/ {print $1 "#" $7 "#" $3}'/ etc/passwd
Root###/bin/bash###0
Operator###/sbin/nologin###1
The usage of 3.BEGIN and END
The usage of 3.1BEGIN
[root@localhost ~] # df-h | grep / $| awk'{print $4}'| awk-F "%" 'BEGIN {print "root_usage!"} {print $1}'
Root_usage!
fourteen
3.2BEGIN and END are used together,\ nto wrap lines.
[root@localhost ~] # df-h | grep / $| awk'{print $4}'| awk-F "%" 'BEGIN {print "\ nroot_usage!"\ n = "} {print $1} END {print" = "}'
Root_usage!
=
fourteen
=
The usage of 4.FS, OFS, NR and NF
4.1FS is equivalent to-F, with columns separated by colons
[root@localhost ~] # awk 'BEGIN {FS= ":"} / root/ {print $1, 3, 5, 7, 5 / etc/passwd
Root 0 root / bin/bash
Operator 11 operator / sbin/nologin
4.2OFS changes the default delimiter to separate columns with a # sign
[root@localhost ~] # awk-F: 'BEGIN {OFS= "#} / root/ {print $1 recorder / etc/passwd
Root###0###root###/bin/bash
Operator###11###operator###/sbin/nologin
The-v option can also be implemented
[root@localhost ~] # awk-F:-v OFS= "#" / root/ {print $1 recorder 3 meme 5 meme 7}'/ etc/passwd
Root###0###root###/bin/bash
Operator###11###operator###/sbin/nologin
The usage of 4.3 semicolon
[root@localhost ~] # awk 'BEGIN {FS= ":"; OFS= "#"} / root/ {print $1 miner 7}' / etc/passwd
Root#/bin/bash
Operator#/sbin/nologin
4.4NR is used to print line numbers, and columns can be printed at custom locations.
[root@localhost ~] # awk-F:'/ root/ {print NR,$1,$7,$5,$3}'/ etc/passwd
1 root / bin/bash root 0
12 operator / sbin/nologin operator 11
[root@localhost ~] # awk'/ root/ {print NR,$0}'/ etc/passwd
1 root:x:0:0:root:/root:/bin/bash
12 operator:x:11:0:operator:/root:/sbin/nologin
4.5 print blank lines
[root@localhost ~] # awk'/ ^ $/ {print NR}'/ etc/passwd
4.6 these two commands are equivalent, but grep is more efficient
[root@localhost ~] # awk'/ root/ {print NR,$0}'/ etc/passwd
1 root:x:0:0:root:/root:/bin/bash
12 operator:x:11:0:operator:/root:/sbin/nologin
[root@localhost ~] # grep-n 'root' / etc/passwd
1:root:x:0:0:root:/root:/bin/bash
12:operator:x:11:0:operator:/root:/sbin/nologin
4.7NF is used to print the number of columns. NF prints out seven columns, and $NF prints the last column.
[root@localhost ~] # awk-F:'/ root/ {print NR,NF,$NF,$0}'/ etc/passwd
1 7 / bin/bash root:x:0:0:root:/root:/bin/bash
12 7 / sbin/nologin operator:x:11:0:operator:/root:/sbin/nologin
Comparison in 5.awk
=
= = equal to
! = not equal to
~ match
! ~ mismatch
5.1 print the first column with 37 rows or more
[root@localhost ~] # awk-F:'NR > = 37 {print NR,$1}'/ etc/passwd
37 xfs
38 gdm
39 pegasus
40 oracle
5.2 print the fourth column greater than or equal to 60
[root@localhost shell] # cat awk.txt
1 80 1 li
2 60 2 wang
3 70 3 zhang
4 10 4 zhao
[root@localhost shell] # awk'$2 > = 60 {print $4} 'awk.txt
Li
Wang
Zhang
5.3 print the fields in the first column that match root
[root@localhost ~] # awk-F:'$1pm = "root" {print $1m 3m 5m 7R 7}'/ etc/passwd
Root 0 root / bin/bash
5.4 print full-text fields that match root
[root@localhost ~] # awk-F:'$0~/root/ {print NR,$1,$7,$5,$3}'/ etc/passwd
1 root / bin/bash root 0
12 operator / sbin/nologin operator 11
5.5 print the fields in the sixth column that match root
[root@localhost] # awk-F:'$6 ~ / root/ {print $1 recorder 5 recorder 6}'/ etc/passwd
Root root / root
Operator operator / root
5.6 print the fields in lines 7 to 12
[root@localhost /] # awk-F: 'NR==7,NR==12 {print NR,$1,$7}' / etc/passwd
7 shutdown / sbin/shutdown
8 halt / sbin/halt
9 mail / sbin/nologin
10 news
11 uucp / sbin/nologin
12 operator / sbin/nologin
6.if judgment
6.1 print if the first column equals root
[root@localhost ~] # awk-F:'{if ($1mm = "root") print $0}'/ etc/passwd
Root:x:0:0:root:/root:/bin/bash
6.2 print the first column that matches the oracle
[root@localhost ~] # cat / etc/passwd | awk'{if ($1 ~ "oracle") print NR,$0}'
40 oracle:x:500:501::/home/oracle:/bin/bash
6.3 print the last column of rows that match bash
[root@localhost ~] # awk-F:'{if ($NF~/bash/) print NR,$1,$NF}'/ etc/passwd
1 root / bin/bash
31 postgres / bin/bash
35 mysql / bin/bash
40 oracle / bin/bash
