筆記

空變數的處理

運算式	說明
${var:-word}	如果變數 var 尚未設定或是 null， 則將使用 word 這個值，但不改變 var 變數的內容。

字串處理

${#var}	return length
${var#word}	cut shortest match from start
${var##word}	cut longest match from start
${var%word}	cut shortest match from end
${var%%word}	cut longest match from end
${var:offset}	return string starting at 'offset'
${var:offset:length}	return 'length' characters starting at 'offset'
${var/pattern/string}	replace single match
${var//pattern/string}	replace all matches

Example:

var="amanuensis"

echo ${#var}
10

echo ${var#*n}  (n=4)
uensis

echo ${var##*n}
sis

echo ${var%n*}
amanue

echo ${var%%n*}
ama

echo ${var:7}
sis

echo ${var:1:3}
man

echo ${var/amanuen/paralip}
paralipsis

echo ${var//a/A}
AmAnuensis

ref:

1. 第二十四章 Shell Script
2. Introduction to Shell Scripting, part 4  (感謝Ryan提供)