Incrementing a variable inside a Bash loop

Question

I m trying to write a small script that will count entries in a log file  and I m incrementing  a variable  USCOUNTER  which I m trying to use after the loop is done    But at that moment USCOUNTER looks to be 0 instead of the actual value  Any idea what I m doing wrong  Thanks   FILE  1  tail -n10 mylog  gt   FILE  USCOUNTER 0  cat  FILE   while read line  do   country   echo   line    cut -d    -f1    if    US      country     then         USCOUNTER  expr  USCOUNTER   1          echo  US counter  USCOUNTER    fi done echo  final  USCOUNTER    It outputs   US counter 1 US counter 2 US counter 3    final 0

User · Accepted Answer

You are using USCOUNTER in a subshell  that s why the variable is not showing in the main shell   Instead of cat FILE   while      do just a while     done  lt   FILE  This way  you avoid the common problem of I set variables in a loop that s in a pipeline  Why do they disappear after the loop terminates  Or  why can t I pipe data to read    while read country    do   if    US      country     then         USCOUNTER   expr  USCOUNTER   1          echo  US counter  USCOUNTER    fi done  lt    FILE    Note I also replaced the    expression with a       I also replaced while read line  do country   echo   line    cut -d    -f1  with while read country    This allows you to say while read var1 var2     varN where var1 contains the first word in the line   var2 and so on  until  varN containing the remaining content

User · Answer

Using the following 1 line command for changing many files name in linux using phrase specificity    find -type f -name    jpg    rename  s holiday honeymoon     For all files with the extension   jpg   if they contain the string  holiday   replace it with  honeymoon   For instance  this command would rename the file  ourholiday001 jpg  to  ourhoneymoon001 jpg    This example also illustrates how to use the find command to send a list of files  -type f  with the extension  jpg  -name    jpg   to rename via a pipe      rename then reads its file list from standard input

User · Answer

You re getting final 0 because your while loop is being executed in a sub  shell  process and any changes made there are not reflected in the current  parent  shell   Correct script   while read -r country    do   if    US      country     then           USCOUNTER             echo  US counter  USCOUNTER    fi done  lt    FILE

User · Answer

USCOUNTER   grep -c   US     FILE

User · Answer

Incrementing a variable can be done like that       my counter     my counter   1    Counting the number of occurrence of a pattern in a column can be done with grep   grep -cE            2 US    -c count            To detect a colonne    2  the colonne number   US your pattern

User · Answer

minimalist  counter 0   counter     echo  counter

User · Answer

I had the same  count variable in a while loop getting lost issue    fedorqui s answer  and a few others  are accurate answers to the actual question  the sub-shell is indeed the problem   But it lead me to another issue  I wasn t piping a file content    but the output of a series of pipes  amp  greps     my erroring sample code   count 0 cat  etc hosts   head   while read line  do     count       echo  count  line done echo  count   and my fix thanks to the help of this thread and the process substitution   count 0 while IFS  read -r line  do     count       echo   count  line  done  lt   lt  cat  etc hosts   head  echo   count

User · Answer

Always use -r with read  There is no need to use cut  you can stick with pure bash solutions    In this case passing read a 2nd var     to catch the additional  fields   Prefer       over      Use arithmetic expressions  Do not forget to quote variables  Link includes other pitfalls as well     while read -r country    do   if     country    US      then       USCOUNTER         echo  US counter  USCOUNTER    fi done  lt    FILE

[bash] Incrementing a variable inside a Bash loop

Examples related to bash

Examples related to shell

Examples related to loops