expr

v0.0.28 
expr [EXPRESSION]
expr [OPTIONS]

Print the value of EXPRESSION to standard output

Options

--version

output version information and exit

--help

display this help and exit

Print the value of EXPRESSION to standard output. A blank line below separates increasing precedence groups.

EXPRESSION may be:

  • ARG1 | ARG2: ARG1 if it is neither null nor 0, otherwise ARG2
  • ARG1 & ARG2: ARG1 if neither argument is null or 0, otherwise 0
  • ARG1 < ARG2: ARG1 is less than ARG2
  • ARG1 <= ARG2: ARG1 is less than or equal to ARG2
  • ARG1 = ARG2: ARG1 is equal to ARG2
  • ARG1 != ARG2: ARG1 is unequal to ARG2
  • ARG1 >= ARG2: ARG1 is greater than or equal to ARG2
  • ARG1 > ARG2: ARG1 is greater than ARG2
  • ARG1 + ARG2: arithmetic sum of ARG1 and ARG2
  • ARG1 - ARG2: arithmetic difference of ARG1 and ARG2
  • ARG1 * ARG2: arithmetic product of ARG1 and ARG2
  • ARG1 / ARG2: arithmetic quotient of ARG1 divided by ARG2
  • ARG1 % ARG2: arithmetic remainder of ARG1 divided by ARG2
  • STRING : REGEXP: anchored pattern match of REGEXP in STRING
  • match STRING REGEXP: same as STRING : REGEXP
  • substr STRING POS LENGTH: substring of STRING, POS counted from 1
  • index STRING CHARS: index in STRING where any CHARS is found, or 0
  • length STRING: length of STRING
  • + TOKEN: interpret TOKEN as a string, even if it is a keyword like match or an operator like /
  • ( EXPRESSION ): value of EXPRESSION

Beware that many operators need to be escaped or quoted for shells. Comparisons are arithmetic if both ARGs are numbers, else lexicographical. Pattern matches return the string matched between ( and ) or null; if ( and ) are not used, they return the number of characters matched or 0.

Exit status is 0 if EXPRESSION is neither null nor 0, 1 if EXPRESSION is null or 0, 2 if EXPRESSION is syntactically invalid, and 3 if an error occurred.

Environment variables:

  • EXPR_DEBUG_TOKENS=1: dump expression's tokens
  • EXPR_DEBUG_RPN=1: dump expression represented in reverse polish notation
  • EXPR_DEBUG_SYA_STEP=1: dump each parser step
  • EXPR_DEBUG_AST=1: dump expression represented abstract syntax tree

Examples

Get the length of a specific string:

expr length "{{string}}"

Get the substring of a string with a specific length:

expr substr "{{string}}" {{from}} {{length}}

Match a specific substring against an anchored pattern:

expr match "{{string}}" '{{pattern}}'

Get the first char position from a specific set in a string:

expr index "{{string}}" "{{chars}}"

Calculate a specific mathematic expression:

expr {{expression1}} {{+|-|*|/|%}} {{expression2}}

Get the first expression if its value is non-zero and not null otherwise get the second one:

expr {{expression1}} \| {{expression2}}

Get the first expression if both expressions are non-zero and not null otherwise get zero:

expr {{expression1}} \& {{expression2}}

The examples are provided by the tldr-pages project under the CC BY 4.0 License.

Please note that, as uutils is a work in progress, some examples might fail.