Shulou(Shulou.com)06/01 Report--

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}'

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The 2.3cut command is also implemented

[root@localhost ~] # df-h | grep / $| awk'{print $4}'| cut-d "%"-f 1

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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!

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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!

=

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=

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

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