SHELL Variable Summary

Positional variables

$ A Gets the file name of the current user script contains the path

$n gets the nth parameter of the currently executing shell script if n is greater than 9 in curly braces ${10}

$# gets the number of arguments for the currently executing shell script

$? Check if the last command is successful, if 0 is returned successfully

0 successes

2 Permission denied

125 script Run Error system related

126 Command not executed

127 No commands to execute

>128 command is forcibly stopped by the system

$$ Process number

BaseName the name of the script

DirName $ $ Script Path

Character matching

${#string} Returns the length of the $string

${string:position} in string, starting from position $position to extract string

${string:position:length} in string, starting from position $position to extract substring of length $length

${string##} removed from the beginning

${string%substring} removed from the end

${STRING/SUBSTRING/REPLAC} replace $replac first match replace $substring

${STRING/%SUBSTRING/REPLAC} replaces $replac first match replacement $substring from the end

${string/#SUBSTRING/replac} replaces $replac first match replacement $substring from the beginning

Wd= "I am a Boy"

echo ${#WD} print string length

Echo ${wd:2} returns after the first character

echo ${wd}|wc-m can also print character lengths

Echo ${wd:0:3} Starts from the No. 0 and takes three

echo ${wd}|cut-c 1-5 take 1-5

Echo ${wd#i} removes the shortest character I from the beginning

echo ${wd# #I} remove the longest character from the beginning I

echo ${wd/i Am/you is} first match replace

Echo ${wd/#} matches from the beginning

Echo ${wd/%} matches from the end

Rename

Defining variables

1.

${value:-word} detects an empty variable and prints it if $string is not defined position

Result=${value:-word}

T=${cron_value:-unset}

["$t"! = "UNSET"] && export cron_value= "$t"

Find ${path:=/tmp/}-name *.tar.gz-type-f |xargs rm-rf

2.

${value:=word} If the variable is not defined, the value is assigned to the variable.

3.

${value:? " Message "} If the variable name exists and is not NULL, the value of the variable is returned. Otherwise, the variable name is displayed: Message

4.

${value:+word} returns Word if the variable name exists and is not NULL, otherwise null is used to detect whether the variable is defined

5.

${value-word} If the variable does not exist in Word instead of vsftpd the following is useful to

SHELL Variable Summary