How to remove trailing spaces from. a variable in a shell script? [duplicate] - bash

Question

I have a shell script with this code:
var=`hg st -R "$path"`
if [ -n "$var" ]; then
echo $var
fi
But the conditional code always executes, because hg st always prints at least one newline character.
Is there a simple way to strip whitespace from $var (like trim() in PHP)?
or
Is there a standard way of dealing with this issue?
I could use sed or AWK, but I'd like to think there is a more elegant solution to this problem.

Answer 1

A simple answer is:
echo " lol " | xargs
Xargs will do the trimming for you. It's one command/program, no parameters, returns the trimmed string, easy as that!
Note: this doesn't remove all internal spaces so "foo bar" stays the same; it does NOT become "foobar". However, multiple spaces will be condensed to single spaces, so "foo bar" will become "foo bar". In addition it doesn't remove end of lines characters.

Answer 2

Let's define a variable containing leading, trailing, and intermediate whitespace:
FOO=' test test test '
echo -e "FOO='${FOO}'"
# > FOO=' test test test '
echo -e "length(FOO)==${#FOO}"
# > length(FOO)==16
How to remove all whitespace (denoted by [:space:] in tr):
FOO=' test test test '
FOO_NO_WHITESPACE="$(echo -e "${FOO}" | tr -d '[:space:]')"
echo -e "FOO_NO_WHITESPACE='${FOO_NO_WHITESPACE}'"
# > FOO_NO_WHITESPACE='testtesttest'
echo -e "length(FOO_NO_WHITESPACE)==${#FOO_NO_WHITESPACE}"
# > length(FOO_NO_WHITESPACE)==12
How to remove leading whitespace only:
FOO=' test test test '
FOO_NO_LEAD_SPACE="$(echo -e "${FOO}" | sed -e 's/^[[:space:]]*//')"
echo -e "FOO_NO_LEAD_SPACE='${FOO_NO_LEAD_SPACE}'"
# > FOO_NO_LEAD_SPACE='test test test '
echo -e "length(FOO_NO_LEAD_SPACE)==${#FOO_NO_LEAD_SPACE}"
# > length(FOO_NO_LEAD_SPACE)==15
How to remove trailing whitespace only:
FOO=' test test test '
FOO_NO_TRAIL_SPACE="$(echo -e "${FOO}" | sed -e 's/[[:space:]]*$//')"
echo -e "FOO_NO_TRAIL_SPACE='${FOO_NO_TRAIL_SPACE}'"
# > FOO_NO_TRAIL_SPACE=' test test test'
echo -e "length(FOO_NO_TRAIL_SPACE)==${#FOO_NO_TRAIL_SPACE}"
# > length(FOO_NO_TRAIL_SPACE)==15
How to remove both leading and trailing spaces--chain the seds:
FOO=' test test test '
FOO_NO_EXTERNAL_SPACE="$(echo -e "${FOO}" | sed -e 's/^[[:space:]]*//' -e 's/[[:space:]]*$//')"
echo -e "FOO_NO_EXTERNAL_SPACE='${FOO_NO_EXTERNAL_SPACE}'"
# > FOO_NO_EXTERNAL_SPACE='test test test'
echo -e "length(FOO_NO_EXTERNAL_SPACE)==${#FOO_NO_EXTERNAL_SPACE}"
# > length(FOO_NO_EXTERNAL_SPACE)==14
Alternatively, if your bash supports it, you can replace echo -e "${FOO}" | sed ... with sed ... <<<${FOO}, like so (for trailing whitespace):
FOO_NO_TRAIL_SPACE="$(sed -e 's/[[:space:]]*$//' <<<${FOO})"

Answer 3

There is a solution which only uses Bash built-ins called wildcards:
var=" abc "
# remove leading whitespace characters
var="${var#"${var%%[![:space:]]*}"}"
# remove trailing whitespace characters
var="${var%"${var##*[![:space:]]}"}"
printf '%s' "===$var==="
Here's the same wrapped in a function:
trim() {
local var="$*"
# remove leading whitespace characters
var="${var#"${var%%[![:space:]]*}"}"
# remove trailing whitespace characters
var="${var%"${var##*[![:space:]]}"}"
printf '%s' "$var"
}
You pass the string to be trimmed in quoted form, e.g.:
trim " abc "
A nice thing about this solution is that it will work with any POSIX-compliant shell.
Reference
Remove leading & trailing whitespace from a Bash variable (original source)

Answer 4

In order to remove all the spaces from the beginning and the end of a string (including end of line characters):
echo $variable | xargs echo -n
This will remove duplicate spaces also:
echo " this string has a lot of spaces " | xargs echo -n
Produces: 'this string has a lot of spaces'

Answer 5

Bash has a feature called parameter expansion, which, among other things, allows string replacement based on so-called patterns (patterns resemble regular expressions, but there are fundamental differences and limitations).
[flussence's original line: Bash has regular expressions, but they're well-hidden:]
The following demonstrates how to remove all white space (even from the interior) from a variable value.
$ var='abc def'
$ echo "$var"
abc def
# Note: flussence's original expression was "${var/ /}", which only replaced the *first* space char., wherever it appeared.
$ echo -n "${var//[[:space:]]/}"
abcdef

Answer 6

Strip one leading and one trailing space
trim()
{
local trimmed="$1"
# Strip leading space.
trimmed="${trimmed## }"
# Strip trailing space.
trimmed="${trimmed%% }"
echo "$trimmed"
}
For example:
test1="$(trim " one leading")"
test2="$(trim "one trailing ")"
test3="$(trim " one leading and one trailing ")"
echo "'$test1', '$test2', '$test3'"
Output:
'one leading', 'one trailing', 'one leading and one trailing'
Strip all leading and trailing spaces
trim()
{
local trimmed="$1"
# Strip leading spaces.
while [[ $trimmed == ' '* ]]; do
trimmed="${trimmed## }"
done
# Strip trailing spaces.
while [[ $trimmed == *' ' ]]; do
trimmed="${trimmed%% }"
done
echo "$trimmed"
}
For example:
test4="$(trim " two leading")"
test5="$(trim "two trailing ")"
test6="$(trim " two leading and two trailing ")"
echo "'$test4', '$test5', '$test6'"
Output:
'two leading', 'two trailing', 'two leading and two trailing'

Answer 7

From Bash Guide section on globbing
To use an extglob in a parameter expansion
#Turn on extended globbing
shopt -s extglob
#Trim leading and trailing whitespace from a variable
x=${x##+([[:space:]])}; x=${x%%+([[:space:]])}
#Turn off extended globbing
shopt -u extglob
Here's the same functionality wrapped in a function (NOTE: Need to quote input string passed to function):
trim() {
# Determine if 'extglob' is currently on.
local extglobWasOff=1
shopt extglob >/dev/null && extglobWasOff=0
(( extglobWasOff )) && shopt -s extglob # Turn 'extglob' on, if currently turned off.
# Trim leading and trailing whitespace
local var=$1
var=${var##+([[:space:]])}
var=${var%%+([[:space:]])}
(( extglobWasOff )) && shopt -u extglob # If 'extglob' was off before, turn it back off.
echo -n "$var" # Output trimmed string.
}
Usage:
string=" abc def ghi ";
#need to quote input-string to preserve internal white-space if any
trimmed=$(trim "$string");
echo "$trimmed";
If we alter the function to execute in a subshell, we don't have to worry about examining the current shell option for extglob, we can just set it without affecting the current shell. This simplifies the function tremendously. I also update the positional parameters "in place" so I don't even need a local variable
trim() {
shopt -s extglob
set -- "${1##+([[:space:]])}"
printf "%s" "${1%%+([[:space:]])}"
}
so:
$ s=$'\t\n \r\tfoo '
$ shopt -u extglob
$ shopt extglob
extglob off
$ printf ">%q<\n" "$s" "$(trim "$s")"
>$'\t\n \r\tfoo '<
>foo<
$ shopt extglob
extglob off

Answer 8

You can trim simply with echo:
foo=" qsdqsd qsdqs q qs "
# Not trimmed
echo \'$foo\'
# Trim
foo=`echo $foo`
# Trimmed
echo \'$foo\'

Answer 9

I've always done it with sed
var=`hg st -R "$path" | sed -e 's/ *$//'`
If there is a more elegant solution, I hope somebody posts it.

Answer 10

With Bash's extended pattern matching features enabled (shopt -s extglob), you can use this:
{trimmed##*( )}
to remove an arbitrary amount of leading spaces.

Answer 11

You can delete newlines with tr:
var=`hg st -R "$path" | tr -d '\n'`
if [ -n $var ]; then
echo $var
done

Answer 12

# Trim whitespace from both ends of specified parameter
trim () {
read -rd '' $1 <<<"${!1}"
}
# Unit test for trim()
test_trim () {
local foo="$1"
trim foo
test "$foo" = "$2"
}
test_trim hey hey &&
test_trim ' hey' hey &&
test_trim 'ho ' ho &&
test_trim 'hey ho' 'hey ho' &&
test_trim ' hey ho ' 'hey ho' &&
test_trim $'\n\n\t hey\n\t ho \t\n' $'hey\n\t ho' &&
test_trim $'\n' '' &&
test_trim '\n' '\n' &&
echo passed

Answer 13

There are a lot of answers, but I still believe my just-written script is worth being mentioned because:
it was successfully tested in the shells bash/dash/busybox shell
it is extremely small
it doesn't depend on external commands and doesn't need to fork (->fast and low resource usage)
it works as expected:
it strips all spaces and tabs from beginning and end, but not more
important: it doesn't remove anything from the middle of the string (many other answers do), even newlines will remain
special: the "$*" joins multiple arguments using one space. if you want to trim & output only the first argument, use "$1" instead
if doesn't have any problems with matching file name patterns etc
The script:
trim() {
local s2 s="$*"
until s2="${s#[[:space:]]}"; [ "$s2" = "$s" ]; do s="$s2"; done
until s2="${s%[[:space:]]}"; [ "$s2" = "$s" ]; do s="$s2"; done
echo "$s"
}
Usage:
mystring=" here is
something "
mystring=$(trim "$mystring")
echo ">$mystring<"
Output:
>here is
something<

Answer 14

This is what I did and worked out perfect and so simple:
the_string=" test"
the_string=`echo $the_string`
echo "$the_string"
Output:
test

Answer 15

If you have shopt -s extglob enabled, then the following is a neat solution.
This worked for me:
text=" trim my edges "
trimmed=$text
trimmed=${trimmed##+( )} #Remove longest matching series of spaces from the front
trimmed=${trimmed%%+( )} #Remove longest matching series of spaces from the back
echo "<$trimmed>" #Adding angle braces just to make it easier to confirm that all spaces are removed
#Result
<trim my edges>
To put that on fewer lines for the same result:
text=" trim my edges "
trimmed=${${text##+( )}%%+( )}

Answer 16

# Strip leading and trailing white space (new line inclusive).
trim(){
[[ "$1" =~ [^[:space:]](.*[^[:space:]])? ]]
printf "%s" "$BASH_REMATCH"
}
OR
# Strip leading white space (new line inclusive).
ltrim(){
[[ "$1" =~ [^[:space:]].* ]]
printf "%s" "$BASH_REMATCH"
}
# Strip trailing white space (new line inclusive).
rtrim(){
[[ "$1" =~ .*[^[:space:]] ]]
printf "%s" "$BASH_REMATCH"
}
# Strip leading and trailing white space (new line inclusive).
trim(){
printf "%s" "$(rtrim "$(ltrim "$1")")"
}
OR
# Strip leading and trailing specified characters. ex: str=$(trim "$str" $'\n a')
trim(){
if [ "$2" ]; then
trim_chrs="$2"
else
trim_chrs="[:space:]"
fi
[[ "$1" =~ ^["$trim_chrs"]*(.*[^"$trim_chrs"])["$trim_chrs"]*$ ]]
printf "%s" "${BASH_REMATCH[1]}"
}
OR
# Strip leading specified characters. ex: str=$(ltrim "$str" $'\n a')
ltrim(){
if [ "$2" ]; then
trim_chrs="$2"
else
trim_chrs="[:space:]"
fi
[[ "$1" =~ ^["$trim_chrs"]*(.*[^"$trim_chrs"]) ]]
printf "%s" "${BASH_REMATCH[1]}"
}
# Strip trailing specified characters. ex: str=$(rtrim "$str" $'\n a')
rtrim(){
if [ "$2" ]; then
trim_chrs="$2"
else
trim_chrs="[:space:]"
fi
[[ "$1" =~ ^(.*[^"$trim_chrs"])["$trim_chrs"]*$ ]]
printf "%s" "${BASH_REMATCH[1]}"
}
# Strip leading and trailing specified characters. ex: str=$(trim "$str" $'\n a')
trim(){
printf "%s" "$(rtrim "$(ltrim "$1" "$2")" "$2")"
}
OR
Building upon moskit's expr soulution...
# Strip leading and trailing white space (new line inclusive).
trim(){
printf "%s" "`expr "$1" : "^[[:space:]]*\(.*[^[:space:]]\)[[:space:]]*$"`"
}
OR
# Strip leading white space (new line inclusive).
ltrim(){
printf "%s" "`expr "$1" : "^[[:space:]]*\(.*[^[:space:]]\)"`"
}
# Strip trailing white space (new line inclusive).
rtrim(){
printf "%s" "`expr "$1" : "^\(.*[^[:space:]]\)[[:space:]]*$"`"
}
# Strip leading and trailing white space (new line inclusive).
trim(){
printf "%s" "$(rtrim "$(ltrim "$1")")"
}

Answer 17

Use AWK:
echo $var | awk '{gsub(/^ +| +$/,"")}1'

Answer 18

You can use old-school tr. For example, this returns the number of modified files in a git repository, whitespaces stripped.
MYVAR=`git ls-files -m|wc -l|tr -d ' '`

Answer 19

This will remove all the whitespaces from your String,
VAR2="${VAR2//[[:space:]]/}"
/ replaces the first occurrence and // all occurrences of whitespaces in the string. I.e. all white spaces get replaced by – nothing

Answer 20

I would simply use sed:
function trim
{
echo "$1" | sed -n '1h;1!H;${;g;s/^[ \t]*//g;s/[ \t]*$//g;p;}'
}
a) Example of usage on single-line string
string=' wordA wordB wordC wordD '
trimmed=$( trim "$string" )
echo "GIVEN STRING: |$string|"
echo "TRIMMED STRING: |$trimmed|"
Output:
GIVEN STRING: | wordA wordB wordC wordD |
TRIMMED STRING: |wordA wordB wordC wordD|
b) Example of usage on multi-line string
string=' wordA
>wordB<
wordC '
trimmed=$( trim "$string" )
echo -e "GIVEN STRING: |$string|\n"
echo "TRIMMED STRING: |$trimmed|"
Output:
GIVEN STRING: | wordAA
>wordB<
wordC |
TRIMMED STRING: |wordAA
>wordB<
wordC|
c) Final note:
If you don't like to use a function, for single-line string you can simply use a "easier to remember" command like:
echo "$string" | sed -e 's/^[ \t]*//' | sed -e 's/[ \t]*$//'
Example:
echo " wordA wordB wordC " | sed -e 's/^[ \t]*//' | sed -e 's/[ \t]*$//'
Output:
wordA wordB wordC
Using the above on multi-line strings will work as well, but please note that it will cut any trailing/leading internal multiple space as well, as GuruM noticed in the comments
string=' wordAA
>four spaces before<
>one space before< '
echo "$string" | sed -e 's/^[ \t]*//' | sed -e 's/[ \t]*$//'
Output:
wordAA
>four spaces before<
>one space before<
So if you do mind to keep those spaces, please use the function at the beginning of my answer!
d) EXPLANATION of the sed syntax "find and replace" on multi-line strings used inside the function trim:
sed -n '
# If the first line, copy the pattern to the hold buffer
1h
# If not the first line, then append the pattern to the hold buffer
1!H
# If the last line then ...
$ {
# Copy from the hold to the pattern buffer
g
# Do the search and replace
s/^[ \t]*//g
s/[ \t]*$//g
# print
p
}'

Answer 21

There are a few different options purely in BASH:
line=${line##+([[:space:]])} # strip leading whitespace; no quote expansion!
line=${line%%+([[:space:]])} # strip trailing whitespace; no quote expansion!
line=${line//[[:space:]]/} # strip all whitespace
line=${line//[[:space:]]/} # strip all whitespace
line=${line//[[:blank:]]/} # strip all blank space
The former two require extglob be set/enabled a priori:
shopt -s extglob # bash only
NOTE: variable expansion inside quotation marks breaks the top two examples!
The pattern matching behaviour of POSIX bracket expressions are detailed here. If you are using a more modern/hackable shell such as Fish, there are built-in functions for string trimming.

Answer 22

I've seen scripts just use variable assignment to do the job:
$ xyz=`echo -e 'foo \n bar'`
$ echo $xyz
foo bar
Whitespace is automatically coalesced and trimmed. One has to be careful of shell metacharacters (potential injection risk).
I would also recommend always double-quoting variable substitutions in shell conditionals:
if [ -n "$var" ]; then
since something like a -o or other content in the variable could amend your test arguments.

Answer 23

Here's a trim() function that trims and normalizes whitespace
#!/bin/bash
function trim {
echo $*
}
echo "'$(trim " one two three ")'"
# 'one two three'
And another variant that uses regular expressions.
#!/bin/bash
function trim {
local trimmed="$#"
if [[ "$trimmed" =~ " *([^ ].*[^ ]) *" ]]
then
trimmed=${BASH_REMATCH[1]}
fi
echo "$trimmed"
}
echo "'$(trim " one two three ")'"
# 'one two three'

Answer 24

This does not have the problem with unwanted globbing, also, interior white-space is unmodified (assuming that $IFS is set to the default, which is ' \t\n').
It reads up to the first newline (and doesn't include it) or the end of string, whichever comes first, and strips away any mix of leading and trailing space and \t characters. If you want to preserve multiple lines (and also strip leading and trailing newlines), use read -r -d '' var << eof instead; note, however, that if your input happens to contain \neof, it will be cut off just before. (Other forms of white space, namely \r, \f, and \v, are not stripped, even if you add them to $IFS.)
read -r var << eof
$var
eof

Answer 25

To remove spaces and tabs from left to first word, enter:
echo " This is a test" | sed "s/^[ \t]*//"
cyberciti.biz/tips/delete-leading-spaces-from-front-of-each-word.html

Answer 26

var=' a b c '
trimmed=$(echo $var)

Answer 27

This is the simplest method I've seen. It only uses Bash, it's only a few lines, the regexp is simple, and it matches all forms of whitespace:
if [[ "$test" =~ ^[[:space:]]*([^[:space:]].*[^[:space:]])[[:space:]]*$ ]]
then
test=${BASH_REMATCH[1]}
fi
Here is a sample script to test it with:
test=$(echo -e "\n \t Spaces and tabs and newlines be gone! \t \n ")
echo "Let's see if this works:"
echo
echo "----------"
echo -e "Testing:${test} :Tested" # Ugh!
echo "----------"
echo
echo "Ugh! Let's fix that..."
if [[ "$test" =~ ^[[:space:]]*([^[:space:]].*[^[:space:]])[[:space:]]*$ ]]
then
test=${BASH_REMATCH[1]}
fi
echo
echo "----------"
echo -e "Testing:${test}:Tested" # "Testing:Spaces and tabs and newlines be gone!"
echo "----------"
echo
echo "Ah, much better."

Answer 28

Removing spaces to one space:
(text) | fmt -su

Answer 29

Assignments ignore leading and trailing whitespace and as such can be used to trim:
$ var=`echo ' hello'`; echo $var
hello

Answer 30

Python has a function strip() that works identically to PHP's trim(), so we can just do a little inline Python to make an easily understandable utility for this:
alias trim='python -c "import sys; sys.stdout.write(sys.stdin.read().strip())"'
This will trim leading and trailing whitespace (including newlines).
$ x=`echo -e "\n\t \n" | trim`
$ if [ -z "$x" ]; then echo hi; fi
hi