Introduction to the use of built-in variables in linux awk

　　Awk is an excellent text processing tool and can be said to be a programming language. The following are the built-in variables of awk that Brothers Linux Training introduces

to you.

　　1. Built-in variable table

　　Attribute description

　　$0 The current record (as a single variable)

　　$1~$n The nth field of the current record, the fields are separated by FS The

　　default input field separator is space

　　NF The number of fields in the current record, which is How many columns are there

　　NR The number of records that have been read, which is the line number, starting from 1

　　RS input records his separator defaults to newline

　　OFS Output field separator defaults to space

　　ORS output record separator, defaults to newline

　　ARGC command The number of line parameters

　　ARGV The command line parameter array

　　FILENAME The name of the current input file

　　IGNORECASE If it is true, the case-ignoring match

　　ARGIND The ARGV identifier of the currently processed file CONVFMT

　　Number conversion format %.6g

　　ENVIRON UNIX environment variable

　　ERRNO UNIX system error message

　　FIELDWIDTHS whitespace-separated string for input field width

　　FNR current record number

　　OFMT number output format %.6g

　　RSTART start of string matched by match function

　　RLENGTH The length of the string matched by the matching function

　　SUBSEP \034

　　2. Example

　　1. Common operations

　　[chengmo@localhost ~]$ awk'/^root/{print $0}' /etc/passwd

　　root:x:0:0:root :/root:/bin/bash

　　/^root/ is the selection expression, $0 means line by line

　　2, set the field separator (FS usage)

　　[chengmo@localhost ~]$ awk'BEGIN{FS=":"} /^root/{print $1,$NF}' /etc/passwd

　　root /bin/bash

　　FS is the field separator, you can set it yourself, the default is space, because passwd is separated by ":", so you need to modify the default separator . NF is the total number of fields, $0 represents the current row record, $1-$n is the current row, and the corresponding value of each field.

　　3. Number of records (NR, FNR usage)

　　[chengmo@localhost ~]$ awk 'BEGIN{FS=":"}{printNR,$1,$NF}' /etc/passwd

　　1 root /bin/bash

　　2 bin /sbin/nologin

　　3 daemon /sbin/nologin

　　4 adm /sbin/nologin

　　5 lp /sbin/nologin

　　6 sync /bin/sync

　　7 shutdown /sbin/shutdown

　　……

　　NR gets the line where the current record is located

　　4. Set the output field separator (OFS usage)

　　[chengmo@localhost ~]$ awk'BEGIN{FS=":";OFS ="^^"}/^root/{print FNR,$1,$NF}'/etc/passwd

　　1^^root^^/bin/bash

　　OFS set the default field separator

　　5, set the output line record separator (ORS How to use)

　　[chengmo@localhost ~]$ awk'BEGIN{FS=":";ORS="^^"}{print FNR,$1,$NF}' /etc/passwd

　　1 root /bin/bash^^2 bin/sbin/nologin^^3 daemon /sbin/nologin^^4 adm /sbin/nologin^^5 lp /sbin/nologin

　　From the above, ORS is a newline by default, here is modified to: "^^", all lines are separated by "^^".

　　6. Obtaining input parameters (used by ARGC and ARGV)

　　[chengmo@localhost ~]$ awk'BEGIN{FS=":";print "ARGC="ARGC;for(k in ARGV) {printk"="ARGV[k] ; }}'





　　1=/etc/passwd

　　ARGC gets the number of all input parameters, ARGV gets the input parameter content, which is an array.

　　7. Get the incoming file name (used by FILENAME)

　　[chengmo@localhost ~]$ awk'BEGIN{FS=":";print FILENAME}{print FILENAME}' /etc/passwd

　　/etc/passwd

　　FILENAME,$0-$ N,NF cannot be used in BEGIN, and BEGIN cannot obtain any variables that operate with file records.

　　8. Obtain linux environment variables (used by ENVIRON)

　　[chengmo@localhost ~]$ awk'BEGIN{print ENVIRON["PATH"];}' /etc/passwd

　　/usr/lib/qt-3.3/bin:/usr/kerberos /bin:/usr/lib/ccache:/usr/lib/icecc/bin:/usr/local/bin:/bin:/usr/bin:/usr/local/sbin:/usr/sbin:/sbin:/ usr/java/jdk1.5.0_17/bin:/usr/java/jdk1.5.0_17/jre/bin:/usr/local/mysql/bin:/home/web97/bin

　　ENVIRON is a sub-canonical array, which can be accessed by the corresponding key value gets its value.

　　9. Output data format setting: (used by OFMT)

　　[chengmo@localhost ~]$ awk'BEGIN{OFMT="%.3f";print 2/3,123.11111111;}' /etc/passwd

　　0.667 123.111

　　OFMT default output format is: %.6g Six decimal places are reserved, modifying OFMT here will Modify the default data output format.

　　10. Specify the separator by width (used by FIELDWIDTHS)

　　[chengmo@localhost ~]$ echo20100117054932 | awk 'BEGIN{FIELDWIDTHS="4 2 2 2 2 3"}{print$1"-"$2"-"$3,$4": "$5":"$6}'

　　FIELDWIDTHS The format is a string of numbers separated by spaces to separate records. FIELDWIDTHS="4 2 2 2 2 2" means that the width of $1 is 4, $2 is 2, and $3 is 2 .... . This time it will ignore: FS separator.

　　11. RSTARTRLENGTH use

　　[chengmo@localhost ~]$ awk'BEGIN{start=match("this is a test",/[az]+$/); print start, RSTART,RLENGTH }'

　　11 11 4

　　[chengmo@localhost ~]$ awk'BEGIN{start=match("this is a test",/^[az]+$/); print start,



　　RSTART is matched to the first position of the regular expression, RLENGTH matches the character length, and it is not found as -1.