Common operation of variable quantum strings

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

${variable:position} in $string, start extracting substrings from position $position

${variable:position:length} in $string, start extracting substrings of length $length from the position $position

${variable#substring} deletes the shortest match $substring substring starting at the beginning of the variable $string

${variable# #substring} deletes the longest matching $substring substring starting at the beginning of the variable $string

${variable%substring} deletes the shortest match $substring substring starting at the end of the variable $string

[[email protected] ~]$ echo ${cc%t*}

Value not set

${variable%%substring} deletes the longest matching $substring substring starting at the end of the variable $string

[[email protected] ~]$ echo ${cc%%t*}

Value not set

${variable/substring/replace} replaces the first matching $substring with replace

#!/bin/shfor i in $ (ls |grep "jpg$");d o i=${i/finished/};echo $idone

Results:

[Email protected] ~]# sh for2.sh stu_10299_1_.jpgstu_10299_2_.jpgstu_10299_3_.jpgstu_10299_4_.jpgstu_10299_5_.jpg

${variable/#substring/replace} if the $string prefix matches $substring, $replace is used instead of matching $substring

${variable/%substring/replace} if $string end matches $substring, use $replace instead of match $substring

#!/bin/shfor i in $ (ls |grep "jpg$");d Oi=${i/%jpg/mp4}done

Results:

[Email protected] ~]# sh for2.sh stu_10299_1_.mp4stu_10299_2_.mp4stu_10299_3_.mp4stu_10299_4_.mp4stu_10299_5_.mp4

V. Substitution of variables

${value:-word} If the variable value has an assignment, use the value of value, and if value is not assigned, use the following word to assign value

${value-word} If the variable value has an assignment, use the value of value, and if value is not assigned or empty, then Word is returned with Word and assigned value

${value:=word} If the variable value has an assignment, use the value of value, and if value is not assigned, use the following word to assign value

${value:+word} If value has an assignment, the value is re-assigned in Word and NULL is returned if value is not assigned.

${value:? " Not defined "} if value is not assigned, then the error defined later is returned, and if value is assigned, nothing is returned. Used to test if a variable has a value

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Common operation of variable quantum strings