Cynical Software

Bash Strings

Create / delete

Create string

a=""

a="abcdef"

abcdef

Initialise

Fixed contents	a=""	a="abcdef"	abcdef
Repeated value 'x' x 10	a=""	a=`printf %10s\|tr \ x`	xxxxxxxxxx

Count

Length of string	a="abc"	i=${#a}	3
Length of string [alternative]	a="abc"	i=`expr length $a`	3
Size of underlying storage	n/a	error	n/a
Number of 'X' chars in string	a="abcXdefXX"	n=`echo "$a" \| tr -cd "X" \| wc -c \| awk '{print $1}'`	3
Number of 'X', 'Y' and 'Z' chars in string	a="abcXdefYZ"	n=`echo "$a" \| tr -cd "XYZ" \| wc -c \| awk '{print $1}'`	3

Retrieve by index

Retrieve 1st char	a="abc"	c=${a:0:1}	a
Retrieve 1st char [alternative]	a="abc"	c=`expr substr $a 1 1`	a
Retrieve last char	a="abc"	c=${a:${#a}-1:1}	c
Retrieve last char [alternative]	a="abc"	c=`expr substr $a ${#a} 1`	c
Retrieve char 'n'	a="abcdef" n=2	c=${a:$n:1}	c
Retrieve char 'n' [alternative]	a="abcdef" n=2	let n1=n+1; c=`expr substr $a $n1 1`	c

Slice

Slice from index 'm' to 'n' (inclusive)	a="abcdefghi" m=3 n=6	s=${a:$m:$n-$m+1}	defg
Slice from index 'n' (inclusive)	a="abcdefghi" n=3	s=${a:$n}	defghi
Slice up to index 'n' (inclusive)	a="abcdefghi" n=3	s=${a:0:$n+1}	abcd

Compare

Test for equality (case sensitive)	a="abcdef" b="abc" t="0"	if [[ "$a" == "$b" ]]; then t="1"; fi	0
Test for equality (case insensitive)	a="abcdef" b="ABCdef" t="0"	if [[ "`echo $a \| tr '[A-Z]' '[a-z]'`" == "`echo $b \| tr '[A-Z]' '[a-z]'`" ]]; then t="1"; fi	1
Test for prefix	a="abcdef" b="abc" t="0"	if [[ `expr $a : "$b.*"` != "0" ]]; then t="1"; fi	1
Test for suffix	a="abcdef" b="def"	if [[ `expr $a : ".*$b"` != "0" ]]; then t="1"; fi	1

Test char 'is in' string	a="abcdefghi" c='c' t="0"	if [[ "`expr index $a $c`" != "0" ]]; then t="1"; fi	1
Test substring 'is in' string	a="abcdefghi" b="abc" t="0"	if [[ "`expr index $a $b`" != "0" ]]; then t="1"; fi	1
Find first occurrence of char	a="abcdefccccc" c='c'	let i=`expr index $a $c`-1	2
Find last occurrence of char	a="abcdefccccc" c='c' a=`echo $a \| rev`	let i=${#a}-`expr index $a $c`	10

Split

Split on char

a="one,two,three"
c=','

ifs=$IFS; IFS=$c sa=($a); IFS=$ifs

one two three

Evaluate

Evaluate empty string	a="" t="0"	if [[ "$a" ]]; then t="1"; fi	0
Evaluate non-empty string	a="abcdef" t="0"	if [[ "$a" ]]; then t="1"; fi	1

Insert

Overwrite

Overwrite char at index 'n'	a="abc" n=1 c='B'	a=${a:0:$n}$c${a:$n+1}	aBc
Overwrite substring at index 'n'	a="abcdefghi" b="DEF" n=3	a=${a:0:$n}$b${a:$n+${#b}}	abcDEFghi

Replace

Replace 1st instance of char 'X' with 'Y'	a="XXXYYYZZZ"	a=${a/X/Y}	YXXYYYZZZ
Replace all instances of char 'X' with 'Y'	a="XXXYYYZZZ"	a=${a//X/Y}	YYYYYYZZZ
Replace 1st instance of substring 'abc' with 'XYZ'	a="abcdefabc"	a=${a/abc/XYZ}	XYZdefabc
Replace all instances of substring 'abc' with 'XYZ'	a="abcdefabc"	a=${a//abc/XYZ}	XYZdefXYZ
Replace all instances of 'X','Y','Z' with 'A','B','C' respectively	a="XXXYYYZZZ"	a=`echo $a \| tr '[XYZ]' '[ABC]'`	AAABBBCCC

Remove by value

Remove 1st instance of char 'X'	a="XXXYYYZZZ"	a=${a/X}	XXYYYZZZ
Remove all instances of char 'X'	a="XXXYYYZZZ"	a=${a//X}	YYYZZZ
Remove 1st instance of substring 'abc'	a="abcdefabc"	a=${a/abc}	defabc
Remove all instances of substring 'abc'	a="abcdefabc"	a=${a//abc}	def
Remove prefix 'abc.'	a="abc.abc.def"	a=${a#abc.}	abc.def
Remove suffix '.def'	a="abc.def.def"	a=${a%.def}	abc.def

Remove by index

Remove 1st char	a="abcdef"	a=${a#?}	bcdef
Remove last char	a="abcdefghi"	a=${a%?}	abcdefgh
Remove char at index 'n'	a="abcdef" n=3	a=${a:0:$n}${a:$n+1}	abcef
Remove chars in index range 'm' to 'n' (inclusive)	a="abcdef" m=2 n=4	a=${a:0:$m}${a:$n+1}	abf
Remove chars from index 'n' onwards (inclusive)	a="abcdefghi" n=3	a=${a:0:$n}	abc
Remove chars up to index 'n' (inclusive)	a="abcdefghi" n=3	a=${a:$n+1}	efghi

Trim

Trim leading white space	a=" abc def "	a=$(echo "$a" \| sed 's/^[ ]*//')	abc def
Trim trailing white space	a=" abc def "	a=$(echo "$a" \| sed 's/[ ]*$//')	abc def
Trim leading and trailing white space	a=" abc def "	a=$(echo "$a" \| sed 's/^[ ]//' \| sed 's/[ ]$//')	abc def

Sort

Convert case

Convert to lower case	a="ABCDEFGHI"	a=`echo $a \| tr '[A-Z]' '[a-z]'`	abcdefghi
Convert to upper case	a="abcdefghi"	a=`echo $a \| tr '[a-z]' '[A-Z]'`	ABCDEFGHI
Convert first char to lower case	a="ABCDEFGHI"	a="`echo ${a:0:1} \| tr '[A-Z]' '[a-z'`${a:1}"	aBCDEFGHI
Convert first char to upper case	a="abcdefghi"	a="`echo ${a:0:1} \| tr '[a-z]' '[A-Z]'`${a:1}"	Abcdefghi