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Manipulating Strings

原创 网络安全 作者:VampireAlchemis 时间:2007-01-13 16:53:10 0 删除 编辑

String Length

${#string}

expr length $string

expr "$string" : '.*'

stringZ=abcABC123ABCabc

echo ${#stringZ}                 # 15
echo `expr length $stringZ`      # 15
echo `expr "$stringZ" : '.*'`    # 15

Length of Matching Substring at Beginning of String

expr match "$string" '$substring'

$substring is a regular expression.

expr "$string" : '$substring'

$substring is a regular expression.

stringZ=abcABC123ABCabc
#       |------|

echo `expr match "$stringZ" 'abc[A-Z]*.2'`   # 8
echo `expr "$stringZ" : 'abc[A-Z]*.2'`       # 8

Index

expr index $string $substring

Numerical position in $string of first character in $substring that matches.

stringZ=abcABC123ABCabc
echo `expr index "$stringZ" C12`             # 6
                                             # C position.

echo `expr index "$stringZ" 1c`              # 3
# 'c' (in #3 position) matches before '1'.

This is the near equivalent of strchr() in C.

Substring Extraction

${string:position}

Extracts substring from $string at $position.

If the string parameter is "*" or "@", then this extracts the positional parameters, [1] starting at position.

${string:position:length}

Extracts $length characters of substring from $string at $position.

stringZ=abcABC123ABCabc
#       0123456789.....
#       0-based indexing.

echo ${stringZ:0}                            # abcABC123ABCabc
echo ${stringZ:1}                            # bcABC123ABCabc
echo ${stringZ:7}                            # 23ABCabc

echo ${stringZ:7:3}                          # 23A
                                             # Three characters of substring.

If the string parameter is "*" or "@", then this extracts a maximum of length positional parameters, starting at position.

echo ${*:2}          # Echoes second and following positional parameters.
echo ${@:2}          # Same as above.

echo ${*:2:3}        # Echoes three positional parameters, starting at second.

expr substr $string $position $length

Extracts $length characters from $string starting at $position.

stringZ=abcABC123ABCabc
#       123456789......
#       1-based indexing.

echo `expr substr $stringZ 1 2`              # ab
echo `expr substr $stringZ 4 3`              # ABC

expr match "$string" '($substring)'

Extracts $substring at beginning of $string, where $substring is a regular expression.

expr "$string" : '($substring)'

Extracts $substring at beginning of $string, where $substring is a regular expression.

stringZ=abcABC123ABCabc

echo `expr match "$stringZ" '(.[b-c]*[A-Z]..[0-9])'`   # abcABC1
echo `expr "$stringZ" : '(.[b-c]*[A-Z]..[0-9])'`       # abcABC1
# Both of the above forms are equivalent.

Substring Removal

${string#substring}

Strips shortest match of $substring from front of $string.

${string##substring}

Strips longest match of $substring from front of $string.

stringZ=abcABC123ABCabc
#       |----|
#       |----------|

echo ${stringZ#a*C}      # 123ABCabc
# Strip out shortest match between 'a' and 'C'.

echo ${stringZ##a*C}     # abc
# Strip out longest match between 'a' and 'C'.

${string%substring}

Strips shortest match of $substring from back of $string.

${string%%substring}

Strips longest match of $substring from back of $string.

stringZ=abcABC123ABCabc
#                    ||
#        |------------|

echo ${stringZ%b*c}      # abcABC123ABCa
# Strip out shortest match between 'a' and 'C', from back of $stringZ.

echo ${stringZ%%b*c}     # a
# Strip out longest match between 'a' and 'C', from back of $stringZ.

Substring Replacement

${string/substring/replacement}

Replace first match of $substring with $replacement.

${string//substring/replacement}

Replace all matches of $substring with $replacement.

stringZ=abcABC123ABCabc

echo ${stringZ/abc/xyz}           # xyzABC123ABCabc
                                  # Replaces first match of 'abc' with 'xyz'.

echo ${stringZ//abc/xyz}          # xyzABC123ABCxyz
                                  # Replaces all matches of 'abc' with # 'xyz'.

${string/#substring/replacement}

If $substring matches front end of $string, substitute $replacement for $substring.

${string/%substring/replacement}

If $substring matches back end of $string, substitute $replacement for $substring.

stringZ=abcABC123ABCabc

echo ${stringZ/#abc/XYZ}          # XYZABC123ABCabc
                                  # Replaces front-end match of 'abc' with 'xyz'.

echo ${stringZ/%abc/XYZ}          # abcABC123ABCXYZ
                                  # Replaces back-end match of 'abc' with 'xyz'.

[@more@]

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