How do I trim leading and trailing whitespace from each line of some output?

Question

I would like to remove all leading and trailing spaces and tabs from each line in an output.

Is there a simple tool like trim I could pipe my output into?

Example file:

test space at back 
 test space at front
TAB at end  
    TAB at front
sequence of some    space in the middle
some empty lines with differing TABS and spaces:





 test space at both ends 

Answer 1

awk '{$1=$1;print}'

or shorter:

awk '{$1=$1};1'

Would trim leading and trailing space or tab characters¹ and also squeeze sequences of tabs and spaces into a single space.

That works because when you assign something to any one field and then try to access the whole record ($0, the thing print prints be default), awk needs to rebuild that record by joining all fields ($1, ..., $NF) with OFS (space by default).

To also remove blank lines, change it to awk 'NF{$1=$1;print}' (where NF as a condition selects the records for which the Number of Fields is non-zero). Do not do awk '$1=$1' as sometimes suggested as that would also remove lines whose first field is any representation of 0 supported by awk (0, 00, -0e+12...)

---

_{¹ and possibly other blank characters depending on the locale and the awk implementation}

Answer 2

The command can be condensed like so if you're using GNU sed:

$ sed 's/^[ \t]*//;s/[ \t]*$//' < file

Example

Here's the above command in action.

$ echo -e " \t   blahblah  \t  " | sed 's/^[ \t]*//;s/[ \t]*$//'
blahblah

You can use hexdump to confirm that the sed command is stripping the desired characters correctly.

$ echo -e " \t   blahblah  \t  " | sed 's/^[ \t]*//;s/[ \t]*$//' | hexdump -C
00000000  62 6c 61 68 62 6c 61 68  0a                       |blahblah.|
00000009

Character classes

You can also use character class names instead of literally listing the sets like this, [ \t]:

$ sed 's/^[[:blank:]]*//;s/[[:blank:]]*$//' < file

Example

$ echo -e " \t   blahblah  \t  " | sed 's/^[[:blank:]]*//;s/[[:blank:]]*$//'

Most of the GNU tools that make use of regular expressions (regex) support these classes (here with their equivalent in the typical C locale of an ASCII-based system (and there only)).

 [[:alnum:]]  - [A-Za-z0-9]     Alphanumeric characters
 [[:alpha:]]  - [A-Za-z]        Alphabetic characters
 [[:blank:]]  - [ \t]           Space or tab characters only
 [[:cntrl:]]  - [\x00-\x1F\x7F] Control characters
 [[:digit:]]  - [0-9]           Numeric characters
 [[:graph:]]  - [!-~]           Printable and visible characters
 [[:lower:]]  - [a-z]           Lower-case alphabetic characters
 [[:print:]]  - [ -~]           Printable (non-Control) characters
 [[:punct:]]  - [!-/:-@[-`{-~]  Punctuation characters
 [[:space:]]  - [ \t\v\f\n\r]   All whitespace chars
 [[:upper:]]  - [A-Z]           Upper-case alphabetic characters
 [[:xdigit:]] - [0-9a-fA-F]     Hexadecimal digit characters

Using these instead of literal sets always seems like a waste of space, but if you're concerned with your code being portable, or having to deal with alternative character sets (think international), then you'll likely want to use the class names instead.

References

• Section 3 of the sed FAQ

Answer 3

xargs without arguments do that.

Example:

trimmed_string=$(echo "no_trimmed_string" | xargs) 

Answer 4

As suggested by Stéphane Chazelas in the accepted answer, you can now
create a script /usr/local/bin/trim:

#!/bin/bash
awk '{$1=$1};1'

and give that file executable rights:

chmod +x /usr/local/bin/trim

Now you can pass every output to trim for example:

cat file | trim

---

(for the comments below: i used this before: while read i; do echo "$i"; done
which also works fine, but is less performant)

Answer 5

If you store lines as variables, you can use bash to do the job:

remove leading whitespace from a string:

shopt -s extglob
printf '%s\n' "${text##+([[:space:]])}"

remove trailing whitespace from a string:

shopt -s extglob
printf '%s\n' "${text%%+([[:space:]])}"

remove all whitespace from a string:

printf '%s\n' "${text//[[:space:]]}"

Answer 6

To remove all leading and trailing spaces from a given line thanks to a 'piped' tool, I can identify 3 different ways which are not completely equivalent. These differences concern the spaces between words of the input line. Depending on the expected behaviour, you'll make your choice.

Examples

To explain the differences, let consider this dummy input line:

"   \t  A   \tB\tC   \t  "

tr

$ echo -e "   \t  A   \tB\tC   \t  " | tr -d "[:blank:]"
ABC

tr is really a simple command. In this case, it deletes any space or tabulation character.

awk

$ echo -e "   \t  A   \tB\tC   \t  " | awk '{$1=$1};1'
A B C

awk deletes leading and tailing spaces and squeezes to a single space every spaces between words.

sed

$ echo -e "   \t  A   \tB\tC   \t  " | sed 's/^[ \t]*//;s/[ \t]*$//'
A       B   C

In this case, sed deletes leading and tailing spaces without touching any spaces between words.

Remark:

In the case of one word per line, tr does the job.

Answer 7

sed -e 's/^[[:space:]]*//' -e 's/[[:space:]]*$//'

If you're reading a line into a shell variable, read does that already unless instructed otherwise.

Answer 8

An answer you can understand in a glance:

#!/usr/bin/env python3
import sys
for line in sys.stdin: print(line.strip()) 

Bonus: replace str.strip([chars]) with arbitrary characters to trim or use .lstrip() or .rstrip() as needed.

Like rubo77's answer, save as script /usr/local/bin/trim and give permissions with chmod +x.

Answer 9

sed is a great tool for that:

                        # substitute ("s/")
sed 's/^[[:blank:]]*//; # parts of lines that start ("^")  with a space/tab 
     s/[[:blank:]]*$//' # or end ("$") with a space/tab
                        # with nothing (/)

You can use it for your case be either piping in the text, e.g.

<file sed -e 's/^[[...

or by acting on it 'inline' if your sed is the GNU one:

sed -i 's/...' file

but changing the source this way is "dangerous" as it may be unrecoverable when it doesn't work right (or even when it does!), so backup first (or use -i.bak which also has the benefit to be portable to some BSD seds)!

Answer 10

You will be adding this to your little Bash library. I can almost bet on it! This has the benefit of not adding a newline character to the end of your output, as will happen with echo throwing off your expected output. Moreover, these solutions are reusable, do not require modifying the shell options, can be called in-line with your pipelines, and are posix compliant. This is the best answer, by far. Modify to your liking.

Output tested with od -cb, something some of the other solutions might want to do with their output.

BTW: The correct quantifier is the +, not the *, as you want the replacement to be triggered upon 1 or more whitespace characters!

ltrim (that you can pipe input into)

function ltrim ()
{
    sed -E 's/^[[:space:]]+//'
}

rtrim (that you can pipe input into)

function rtrim ()
{
    sed -E 's/[[:space:]]+$//'
}

trim (the best of both worlds and yes, you can pipe to it)

function trim ()
{
    ltrim | rtrim
}

Update: I have improved this solution to use bash native constructs. The Stream Editor (sed) is not required. You can use shell expansions to achieve what you want, and it works better than the sed solution!

Bash Reference Manual -- Shell Expansions

Answer 11

If the string one is trying to trim is short and continuous/contiguous, one can simply pass it as a parameter to any bash function:

    trim(){
        echo $@
    }

    a="     some random string   "

    echo ">>`trim $a`<<"
Output
>>some random string<<

Answer 12

Using Raku (formerly known as Perl_6):

raku -ne '.trim.put;'

Or more simply:

raku -pe '.=trim;'

As a previous answer suggests (thanks, @Jeff_Clayton!), you can create a trim alias in your bash environment:

alias trim="raku -pe '.=trim;'"

Finally, to only remove leading/trailing whitespace (e.g. unwanted indentation), you can use the appropriate trim-leading or trim-trailing command instead.

https://raku.org/

Answer 13

translate command would work

cat file | tr -d [:blank:]

Answer 14

trimpy () {
    python3 -c 'import sys
for line in sys.stdin: print(line.strip())'
}
trimsed () {
gsed -e 's/^[[:space:]]*//' -e 's/[[:space:]]*$//'
}
trimzsh () {
   local out="$(</dev/stdin)"
   [[ "$out" =~ '^\s*(.*\S)\s*$' ]] && out="$match[1]"  || out=''
   print -nr -- "$out"
}
# example usage
echo " hi " | trimpy

Bonus: replace str.strip([chars]) with arbitrary characters to trim or use .lstrip() or .rstrip() as needed.

Answer 15

I wrote this shell function using awk

awkcliptor(){
    awk -e 'BEGIN{ RS="^$" } {gsub(/^[\n\t ]*|[\n\t ]*$/,"");print ;exit}' "$1" ; } 

BEGIN{ RS="^$" }:
in the beginning before start parsing set record
separator to none i.e. treat the whole input as
a single record

gsub(this,that):
substitute this regexp with that string

/^[\n\t ]*|[\n\t ]*$/:
of that string catch any pre newline space and tab class
or post newline space and tab class and replace them with
empty string

print;exit: then print and exit

"$1":
and pass the first argument of the function to be
process by awk

how to use:
copy above code , paste in shell, and then enter to
define the function.
then you can use awkcliptor as a command with first argument as the input file

sample usage:

echo '
 ggggg    

      ' > a_file
awkcliptor a_file

output:

ggggg

or

echo -e "\n ggggg    \n\n      "|awkcliptor 

output:

ggggg

Answer 16

For those of us without enough space in the brain to remember obscure sed syntax, just reverse the string, cut the 1st field with a delimiter of space, and reverse it back again.

cat file | rev | cut -d' ' -f1 | rev

Answer 17

My favorite is using perl: perl -n -e'/[\s]*(.*)?[\s]*/ms && print $1'

Take for example:

MY_SPACED_STRING="\n\n   my\nmulti-line\nstring  \n\n"

echo $MY_SPACED_STRING

Would output:

   my
multi-line
string  

Then:

echo $MY_SPACED_STRING | perl -n -e'/[\s]*(.*)?[\s]*/ms && print $1'

Would output:

my
multi-line
string 

Answer 18

for bash example:

alias trim="awk '{\$1=\$1};1'"

usage:

echo -e  "    hello\t\tkitty   " | trim | hexdump  -C

result:

00000000  68 65 6c 6c 6f 20 6b 69  74 74 79 0a              |hello kitty.|
0000000c

Answer 19

Remove start space and tab and end space and tab:

alias strip='python3 -c "from sys import argv; print(argv[1].strip(\" \").strip(\"\t\"))"'

Remove every space and tab

alias strip='python3 -c "from sys import argv; print(argv[1].replace(\"\t\", \"\").replace(\" \", \"\")"'

Give argument to strip. Use sys.stdin().read() to make pipeable instead of argv.

Answer 20

simple enough for my purposes was this:

_text_="    one    two       three         "

echo "$_text_" | { read __ ; echo ."$__". ; }

... giving ...

.one    two       three.

... if you want to squeeze the spaces then ...

echo .$( echo $_text_ ).

... gives ...

.one two three.

Answer 21

rust sd command sd '^\s*(.*)\s*' '$1'