仅使用 bash/标准 Linux 命令去除字符串中的单引号和双引号

Question

I'm looking for something that will translate a string as follows, using only bash / standard Linux commands:

1. Single-quotes surrounding a string should be removed
2. Double-quotes surrounding a string should be removed
3. Unquoted strings should remain the same
4. Strings with unmatched surrounding quotes should remain the same
5. Single-quotes that don't surround the string should remain
6. Double-quotes that don't surround the string should remain

For example:

• 'Food' should become Food
• "Food" should become Food
• Food should remain the same
• 'Food" should remain the same
• "Food' should remain the same
• 'Fo'od' should become Fo'od
• "Fo'od" should become Fo'od
• Fo'od should remain the same
• 'Fo"od' should become Fo"od
• "Fo"od" should become Fo"od
• Fo"od should remain the same

Thank you!

Answer 1

This should do it:

sed "s/^\([\"']\)\(.*\)\1\$/\2/g" in.txt

Where in.txt is:

"Fo'od'
'Food'
"Food"
"Fo"od'
Food
'Food"
"Food'
'Fo'od'
"Fo'od"
Fo'od
'Fo"od'
"Fo"od"
Fo"od

And expected.txt is:

"Fo'od'
Food
Food
"Fo"od'
Food
'Food"
"Food'
Fo'od
Fo'od
Fo'od
Fo"od
Fo"od
Fo"od

You can check they match with:

diff -s <(sed "s/^\([\"']\)\(.*\)\1\$/\2/g" in.txt) expected.txt

Answer 2

You could use tr :

echo "$string" | tr -d 'chars to delete' 

... also works, however 'tr' is known to be problematic on much older (circa Redhat 9-ish) distributions. tr is an abbreviation for 'translate', commonly used in pipes to transform input. The -d option simply means 'delete'.

Most modern versions also contain predefined macros to transform upper to lower, lower to upper, kill white space, etc. Hence, if you use it, take a second to poke at what else it does (see the help output / man page), comes in handy.

Answer 3

VAR="'FOOD'"

VAR=$(eval echo $VAR)

Explanation: Since quotes are already understood by the shell you can ask the shell to evaluate a command that just echos the quoted string, the same way it does when you type it yourself.

Here, eval echo $VAR expands to eval echo 'FOOD' because the quotes are actually part of the value of VAR . If you were to run echo 'FOOD' into the shell you'd get FOOD (without the quotes). That's what eval does: it takes its input and runs it like a shell command.

⚠CODE INJECTION!

eval expose scripts to code injection.

 VAR=';ls -l' VAR=$(eval echo $VAR)

will cause execution of ls -l .

Much more harmful codes could be injected here.

Answer 4

您可能想使用sed ...

echo $mystring | sed -s "s/^\(\(\"\(.*\)\"\)\|\('\(.*\)'\)\)\$/\\3\\5/g"

Answer 5

Just using Bash builtins (ie Bash parameter expansion):

IFS=' ' 

food_strings=( "'Food'" '"Food"' Food "'Food\"" "\"Food'" "'Fo'od'" "\"Fo'od\"" "Fo'od" "'Fo\"od'" '"Fo"od"' 'Fo"od'  )  

for food in ${food_strings[@]}; do 

   [[ "${food#\'}" != "$food" ]] && [[ "${food%\'}" != "$food" ]] && { food="${food#\'}"; food="${food%\'}"; } 

   [[ "${food#\"}" != "$food" ]] && [[ "${food%\"}" != "$food" ]] && { food="${food#\"}"; food="${food%\"}"; } 

   echo "$food"

done 

For yet another example of Bash parameter expansion see:

http://codesnippets.joyent.com/posts/show/1816

Answer 6

Just stumbled upon this as well. For the first three test cases, eval echo $string works well. To get it to work for all cases requested and a few others, I came up with this (tested with bash and dash ):

#!/bin/sh

stripquotes() {
    local firstchar="`substr "$1" 0 1`"
    local len=${#1}
    local ilast=$((${#1} - 1))
    local lastchar="`substr "$1" $(($len - 1))`"
    if [ "$firstchar" = '"' ] || [ "$firstchar" = "'" ] && [ $firstchar = $lastchar ]; then
        echo "`substr "$1" 1 $(($len - 2))`"
    else
        echo "$1"
    fi
}

# $1 = String.
# $2 = Start index.
# $3 = Length (optional). If unspecified or an empty string, the length of the
#      rest of the string is used.
substr() {
    local "len=$3"
    [ "$len" = '' ] && len=${#1}
    if ! (echo ${1:$2:$len}) 2>/dev/null; then
        echo "$1" | awk "{ print(substr(\$0, $(($2 + 1)), $len)) }"
    fi
}

var="'Food'"
stripquotes "$var"

var='"Food"'
stripquotes "$var"

var=Food
stripquotes "$var"

var=\'Food\"
stripquotes "$var"

var=\"Food\'
stripquotes "$var"

var="'Fo'od'"
stripquotes "$var"

var="\"Fo'od\""
stripquotes "$var"

var="Fo'od"
stripquotes "$var"

var="'Fo\"od'"
stripquotes "$var"

var="\"Fo\"od\""
stripquotes "$var"

var="Fo\"od"
stripquotes "$var"

# A string with whitespace should work too.
var="'F\"o 'o o o' o\"d'"
stripquotes "$var"

# Strings that start and end with the same character that isn't a quote or
# doublequote should stay the same.
var="TEST"
stripquotes "$var"

# An empty string should not cause errors.
var=
stripquotes "$var"

# Strings of length 2 that begin and end with a quote or doublequote should not
# cause errors.
var="''"
stripquotes "$var"
var='""'
stripquotes "$var"

Answer 7

python -c "import sys;a=sys.stdin.read();a=a.strip();print (a[1:-1] if a[0]==a[-1] and a[0] in \"'\\\"\" else a)"

it doesn't handle edge cases extremely well (such as an empty string), but it will serve as a starting point. It works by striping the front and back character if they are the same and if they are ' or "