Examples

expr 5 + 10 / 2

Addition happens first; result is 7 (truncated from 7.5):

expr \( 5 + 10 \) / 2

Add 1 to variable i; this is how variables are incremented in shell scripts:

i=`expr $i + 1`

expr $a = hello

expr $b + 5 \>= 10

expr $p : '.*'        Result is 11

expr $p : '\(.*\)'    Result is "version.100"

Print the number of lowercase letters at the beginning of p:

expr $p : '[a-z]*'     Result is 7

Match the lowercase letters at the beginning of p:

expr $p : '\([a-z]*\)' Result is "version"

expr "$x" : '\(.....\)' \| "$x"

mv "$x" `expr "$x" : '\(.....\)' \| "$x"`

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Reference: expand		Reference: exstr

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