How to test if string exists in file with Bash

Question

I have a file that contains directory names   my list txt     tmp  var tmp   I d like to check in Bash before I ll add a directory name if that name already exists in the file

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Three methods in my mind   1  Short test for a name in a path  I m not sure this might be your case   ls -a  path    grep  name     2  Short test for a string in a file  grep -R  string   filepath     3  Longer bash script using regex      bin bash  declare file  content txt  declare regex   s string s    declare file content    cat    file     if       file content       regex      please note the space before and after the file content     then         echo  found      else         echo  not found  fi  exit   This should be quicker if you have to test multiple string on a file content using a loop for example changing the regex at any cicle

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grep -E   string    path to file    echo  no match found    -E option makes grep use regular expressions

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My version using fgrep    FOUND  fgrep -c  FOUND   VALIDATION FILE    if    FOUND -eq 0    then     echo  Not able to find    else     echo  able to find         fi

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grep -Fxq  String to be found    ls -a    grep will helps you to check content   ls will list all the Files

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I was looking for a way to do this in the terminal and filter lines in the normal  quot grep behaviour quot   Have your strings in a file strings txt  string1 string2      Then you can build a regular expression like  string1 string2      and use it for filtering  cmd1   grep -P  quot    cat strings txt   tr   n        head -c -1   quot    cmd2  Edit  Above only works if you don t use any regex characters  if escaping is required  it could be done like  cat strings txt   python3 -c  quot import re  sys   sys stdout write re escape line  -1       n   for line in sys stdin  quot

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A grep-less solution  works for me    MY LIST    cat  path to my list txt      if       MY LIST          NEW DIRECTORY NAME        then   echo  It s there   else echo  its not there  fi   based on  https   stackoverflow com a 229606 3306354

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grep -Fxq  quot  FILENAME quot  my list txt  The exit status is 0  true  if the name was found  1  false  if not  so  if grep -Fxq  quot  FILENAME quot  my list txt then       code if found else       code if not found fi  Explanation Here are the relevant sections of the man page for grep   grep  options  PATTERN  FILE      -F  --fixed-strings                 Interpret PATTERN as a list of fixed strings  separated by  newlines  any of which is to be matched  -x  --line-regexp                 Select only those matches that exactly match the whole line  -q  --quiet  --silent                 Quiet  do not write anything to standard output  Exit immediately  with  zero status if any match is found  even if an error  was detected  Also see the -s or --no-messages option   Error handling As rightfully pointed out in the comments  the above approach silently treats error cases as if the string was found  If you want to handle errors in a different way  you ll have to omit the -q option  and detect errors based on the exit status   Normally  the exit status is 0 if selected lines are found and 1 otherwise  But the exit status is 2 if an error occurred  unless the -q or --quiet or --silent option is used and a selected line is found  Note  however  that POSIX only mandates  for programs such as grep  cmp  and diff  that the exit status in case of error be greater than 1  it is therefore advisable  for the sake of portability  to use logic that tests for this general condition instead of strict equality with 2   To suppress the normal output from grep  you can redirect it to  dev null  Note that standard error remains undirected  so any error messages that grep might print will end up on the console as you d probably want  To handle the three cases  we can use a case statement  case  grep -Fx  quot  FILENAME quot   quot  LIST quot   gt  dev null  echo     in   0        code if found          1        code if not found                   code if an error occurred        esac

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Slightly similar to other answers but does not fork cat and entries can contain spaces contains             quot    list      quot      quot    1   quot      amp  amp  echo  contains     echo  does not contain     IFS    r n  list     lt my list txt    so  for a my list txt like  tmp  var tmp  Users usr dir with spaces  these tests contains   tmp  contains   bin  contains   var tmp  contains   Users usr dir with spaces  contains  dir with spaces   return exists does not exist exists exists does not exist

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If you just want to check the existence of one line  you do not need to create a file  E g     if grep -xq  LINE TO BE MATCHED  FILE TO LOOK IN   then     code for if it exists else     code for if it does not exist fi

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The  Thomas s solution didn t work for me for some reason but I had longer string with special characters and whitespaces so I just changed the parameters like this   if grep -Fxq  string you want to find    path to file   then     echo  Found  else     echo  Not found  fi   Hope it helps someone

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Simpler way   if grep   filename  my list txt  gt   dev null then        found else        not found fi   Tip  send to  dev null if you want command s exit status  but not outputs

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Regarding the following solution   grep -Fxq   FILENAME  my list txt   In case you are wondering  as I did  what -Fxq means in plain English    F  Affects how PATTERN is interpreted  fixed string instead of a regex  x  Match whole line q  Shhhhh    minimal printing   From the man file   -F  --fixed-strings     Interpret  PATTERN  as  a  list of fixed strings  separated by newlines  any of which is to be matched       -F is specified by POSIX   -x  --line-regexp     Select only those matches that exactly match the whole line    -x is specified by POSIX   -q  --quiet  --silent     Quiet  do not write anything to standard output   Exit immediately with zero status  if  any  match  is           found   even  if  an error was detected   Also see the -s or --no-messages option    -q is specified by           POSIX

User · Answer

Easiest and simplest way would be   isInFile   cat file txt   grep -c  string     if    isInFile -eq 0    then     string not contained in file else     string is in file at least once fi   grep -c will return the count of how many times the string occurs in the file

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if grep -q   Filename   my list txt    then      echo  exist  else       echo  not exist  fi

User · Answer

If I understood your question correctly  this should do what you need    you can specifiy the directory you would like to add through  check variable if the directory is already in the list  the output is  dir already listed  if the directory is not yet in the list  it is appended to my list txt   In one line  check   tmp newdirectory      -n   grep    check    my list txt      amp  amp  echo  dir already listed     echo   check   gt  gt  my list txt

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Here s a fast way to search and evaluate a string or partial string  if grep -R  quot my-search-string quot   my file ext then       string exists else       string not found fi  You can also test first  if the command returns any results by running only  grep -R  quot my-search-string quot   my file ext

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