How to retrieve the first word of the output of a command in bash

Question

I have a command  for example  echo  word1 word2   I want to put a pipe     and get word1 from the command   echo  word1 word2          I don t know what to put after the pipe

User · Answer

You could try awk  echo  word1 word2    awk    print  1      With awk it is really easy to pick any word you like   1   2

User · Answer

I think one efficient way is the use of bash arrays    array    string     do not use quotes in order to allow word expansion echo   array 0      You can retrieve any word  Index runs from 0 to length-1   Also  you can directly read arrays in a pipe-line   echo  word1 word2    while read -a array  do echo    array 0      done

User · Answer

If you are sure there are no leading spaces  you can use bash parameter substitution     string  word1  word2    echo   string        word1   Watch out for escaping the single space  See here for more examples of substitution patterns  If you have bash   3 0  you could also use regular expression matching to cope with leading spaces - see here     string    word1   word2         string                      echo   BASH REMATCH 1   word1

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echo  word1 word2 word3      read first rest   echo  first       This has the advantage that is not using external commands and leaves the  1   2  etc  variables intact

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echo  word1 word2    cut -f 1 -d       cut cuts the 1st field  -f 1  from a list of fields delimited by the string      -d

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no need to use external commands  Bash itself can do the job  Assuming  word1 word2  you got from somewhere and stored in a variable  eg    string  word1 word2    set --  string   echo  1 word1   echo  2 word2   now you can assign  1  or  2 etc to another variable if you like

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As perl incorporates awk s functionality this can be solved with perl too   echo   word1 word2    perl -lane  print  F 0

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read is your friend    If string is in a variable   string  word1 word2  read -r first    lt  lt  lt    string  printf   s n    first   If you re working in a pipe  first case  you only want the first word of the first line   printf   s n   word1 word2   line2      read -r first    printf   s n    first       second case  you want the first word of each line   printf   s n   word1 word2   worda wordb    while read -r first    do printf   s n    first   done    These work if there are leading spaces   printf   s n      word1 word2      read -r first    printf   s n    first

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I wondered how several of the top answers measured up in terms of speed  I tested the following   1  mattbh s  echo         awk   print  1      2  ghostdog74 s  string        set --  string  echo  1   3  boontawee-home s  echo           read -a array   echo   array 0         and 4  boontawee-home s  echo           read first     echo  first       I measured them with Python s timeit in a Bash script in a Zsh terminal on macOS  using a test string with 215 5-letter words  Did each measurement five times  the results were all for 100 loops  best of 3   and averaged the results   method       time -------------------------------- 1  awk       9 2ms 2  set       11 6ms  1 26    1   3  read -a   11 7ms  1 27    1   4  read      13 6ms  1 48    1     Nice job  voters  The votes  as of this writing  match the solutions  speed

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I was working with a embedded device which had neither perl  awk or python and did it with sed instead  It supports multiple spaces before the first word  which the cut and bash solutions did not handle    VARIABLE    first word with spaces before and after  another word    echo  VARIABLE   sed  s                1     This was very useful when grepping ps for process IDs since the other solutions here using only bash was not able to remove the first spaces which ps uses to align

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Awk is a good option if you have to deal with trailing whitespace because it ll take care of it for you   echo     word1  word2     awk   print  1      Prints  word1    Cut won t take care of this though   echo    word1  word2     cut -f 1 -d       Prints nothing whitespace    cut  here prints nothing whitespace  because the first thing before a space was another space

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Using shell parameter expansion      Here is another solution using shell parameter expansion  It takes care of multiple spaces after the first word  Handling spaces in front of the first word requires one additional expansion  string  word1    word2  echo   string      word1  string  word1    word2        echo   string      word1  Explanation The    signifies deleting the longest possible match of     a space followed by any number of whatever other characters  in the trailing part of string

[bash] How to retrieve the first word of the output of a command in bash?

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