syntaxe d'affectation à une variable

**David_LeNovis** · 28/07/2011, 17h05

Bonjour,

Je débute dans le scripting shell ,et en lisant les scripts de mon prédécesseur je bloque sur cette syntaxe d'affectation.

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VERBE=${1:-put}	
IDENT=${2:-ALL}

Merci par avance,

Invité · 28/07/2011, 17h11

Salut,

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man bash

${parameter:-word}
Use Default Values. If parameter is unset or null, the expansion of word is substituted. Otherwise, the value of parameter is substituted.
${parameter:=word}
Assign Default Values. If parameter is unset or null, the expansion of word is assigned to parameter. The value of parameter is then sub-
stituted. Positional parameters and special parameters may not be assigned to in this way.
${parameter

word}
Display Error if Null or Unset. If parameter is null or unset, the expansion of word (or a message to that effect if word is not present)
is written to the standard error and the shell, if it is not interactive, exits. Otherwise, the value of parameter is substituted.
${parameter:+word}
Use Alternate Value. If parameter is null or unset, nothing is substituted, otherwise the expansion of word is substituted.
${parameter:offset}
${parameter:offset:length}
Substring Expansion. Expands to up to length characters of parameter starting at the character specified by offset. If length is omitted,
expands to the substring of parameter starting at the character specified by offset. length and offset are arithmetic expressions (see
ARITHMETIC EVALUATION below). length must evaluate to a number greater than or equal to zero. If offset evaluates to a number less than
zero, the value is used as an offset from the end of the value of parameter. Arithmetic expressions starting with a - must be separated by
whitespace from the preceding : to be distinguished from the Use Default Values expansion. If parameter is @, the result is length posi-
tional parameters beginning at offset. If parameter is an indexed array name subscripted by @ or *, the result is the length members of the
array beginning with ${parameter[offset]}. A negative offset is taken relative to one greater than the maximum index of the specified
array. Substring expansion applied to an associative array produces undefined results. Note that a negative offset must be separated from
the colon by at least one space to avoid being confused with the :- expansion. Substring indexing is zero-based unless the positional
parameters are used, in which case the indexing starts at 1 by default. If offset is 0, and the positional parameters are used, $0 is pre-
fixed to the list.