How to remove a newline from a string in Bash

Question

I have the following variable   echo    COMMAND     which returns     REBOOT    How can I remove that first newline

User · Answer

Adding answer to show example of stripping multiple characters including \r using tr and using sed. And illustrating using hexdump.

In my case I had found that a command ending with awk print of the last item |awk '{print $2}' in the line included a carriage-return \r as well as quotes.

I used sed 's/["\n\r]//g' to strip both the carriage-return and quotes.

I could also have used tr -d '"\r\n'.

Interesting to note sed -z is needed if one wishes to remove \n line-feed chars.

$ COMMAND=$'\n"REBOOT"\r   \n'

$ echo "$COMMAND" |hexdump -C
00000000  0a 22 52 45 42 4f 4f 54  22 0d 20 20 20 0a 0a     |."REBOOT".   ..|

$ echo "$COMMAND" |tr -d '"\r\n' |hexdump -C
00000000  52 45 42 4f 4f 54 20 20  20                       |REBOOT   |

$ echo "$COMMAND" |sed 's/["\n\r]//g' |hexdump -C
00000000  0a 52 45 42 4f 4f 54 20  20 20 0a 0a              |.REBOOT   ..|

$ echo "$COMMAND" |sed -z 's/["\n\r]//g' |hexdump -C
00000000  52 45 42 4f 4f 54 20 20  20                       |REBOOT   |

And this is relevant: What are carriage return, linefeed, and form feed?

CR == \r == 0x0d
LF == \n == 0x0a

User · Answer

If you are using bash with the extglob option enabled  you can remove just the trailing whitespace via   shopt -s extglob COMMAND    nRE BOOT r    n  echo     COMMAND        t r n          This outputs     RE BOOT    Or replace    with    to replace just the leading whitespace

User · Answer

You can simply use echo -n    COMMAND

User · Answer

Clean your variable by removing all the carriage returns   COMMAND   echo  COMMAND tr -d   n

User · Answer

What worked for me was echo  testVar   tr   n       Where  testVar contained my variable script-output

User · Answer

echo    COMMAND   tr   n        will replace the newline  in POSIX Unix it s not a carriage return  with a space   To be honest I would think about switching away from bash to something more sane though  Or avoiding generating this malformed data in the first place   Hmmm  this seems like it could be a horrible security hole as well  depending on where the data is coming from

User · Answer

Using bash   echo     COMMAND    n        Note that the control character in this question is a  newline    n   not a carriage return   r   the latter would have output REBOOT  on a single line    Explanation  Uses the Bash Shell Parameter Expansion   parameter pattern string       The pattern is expanded to produce a pattern just as in filename expansion  Parameter is expanded and the longest match of pattern against its value is replaced with string        If string is null  matches of pattern are deleted and the   following pattern may be omitted    Also uses the     ANSI-C quoting construct to specify a newline as    n   Using a newline directly would work as well  though less pretty   echo     COMMAND        Full example     bin bash COMMAND     n REBOOT  echo     COMMAND    n       Outputs  REBOOT    Or  using newlines      bin bash COMMAND   REBOOT  echo     COMMAND        Outputs  REBOOT

User · Answer

Under bash  there are some bashisms   The tr command could be replaced by    bashism   COMMAND    nREBOOT r    n  echo     COMMAND         OOT    echo     COMMAND      t r n       REBOOT      echo     COMMAND      t r n        REBOOT    See Parameter Expansion and QUOTING in bash s man page   man -Pless      pattern bash man -Pless        string     bash  man -Pless          Parameter    Exp bash man -Pless          QUOTING bash   Further     As asked by  AlexJordan  this will suppress all specified characters  So what if  COMMAND do contain spaces     COMMAND             n        RE BOOT       r            n  echo    COMMAND                BOOT          CLEANED   COMMAND      t r n    echo    CLEANED                     RE BOOT                    shopt -q extglob      echo  Set shell option  extglob  on   shopt -s extglob    CLEANED   CLEANED        echo    CLEANED                     RE BOOT   CLEANED   CLEANED        echo    CLEANED    RE BOOT    Shortly   COMMAND             n        RE BOOT       r            n  CLEANED   COMMAND      t r n     amp  amp  CLEANED   CLEANED        echo     CLEANED           RE BOOT    Note  bash have extglob option to be enabled  shopt -s extglob  in order to use        syntax

User · Answer

To address one possible root of the actual issue  there is a chance you are sourcing a crlf file  CRLF Example   env  crlf  VARIABLE A  quot abc quot  VARIABLE B  quot def quot   run sh    bin bash source  env echo  quot  VARIABLE A quot  echo  quot  VARIABLE B quot  echo  quot  VARIABLE A  VARIABLE B quot   Returns  abc def  def  If however you convert to LF   env  lf  VARIABLE A  quot abc quot  VARIABLE B  quot def quot   run sh    bin bash source  env echo  quot  VARIABLE A quot  echo  quot  VARIABLE B quot  echo  quot  VARIABLE A  VARIABLE B quot   Returns  abc def abc def

[bash] How to remove a newline from a string in Bash

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