How do I write a for loop in bash

Question

I m looking for the basic loop like   for int i   0  i  lt  MAX  i        doSomething i       but for bash

User · Answer

Bash 3 0  can use this syntax   for i in  1  10    do       done     which avoids spawning an external program to expand the sequence  such as seq 1 10    Of course  this has the same problem as the for     solution  being tied to bash and even a particular version  if this matters to you

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if you re intereased only in bash the  for           solution presented above is the best  but if you want something POSIX SH compliant that will work on all unices you ll have to use  expr  and  while   and that s because        or  seq  or  i i 1  are not that portable among various shells

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I use variations of this all the time to process files        for files in   log  do echo  Do stuff with   files   echo  Do more stuff with   files   done    If processing lists of files is what you re interested in  look into the -execdir option for files

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The bash for consists on a variable  the iterator  and a list of words where the iterator will  well  iterate   So  if you have a limited list of words  just put them in the following syntax   for w in word1 word2 word3 do   doSomething  w  done   Probably you want to iterate along some numbers  so you can use the seq command to generate a list of numbers for you   from 1 to 100 for example   seq 1 100   and use it in the FOR loop   for n in   seq 1 100  do   doSomething  n  done   Note the        syntax  It s a bash behaviour  it allows you to pass the output from one command  in our case from seq  to another  the for   This is really useful when you have to iterate over all directories in some path  for example   for d in   find  somepath -type d  do   doSomething  d  done   The possibilities are infinite to generate the lists

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bin bash  function do something      echo value   1     MAX 4 for    i 0  i lt MAX  i             do something   i        Here s an example that can also work in older shells  while still being efficient for large counts   Z   date  awk  BEGIN   for   i 0  i lt 4  i       print i  hello  ENVIRON  Z           But good luck doing useful things inside of awk  How do I use shell variables in an awk script

User · Answer

for   i   0   i  lt  max   i       do echo   i   done

User · Answer

From this site   for i in   seq 1 10   do     echo  i done

User · Answer

Try the bash built-in help      help for  for  for NAME  in WORDS        do COMMANDS  done     The  for  loop executes a sequence of commands for each member in a     list of items   If  in WORDS       is not present  then  in       is     assumed   For each element in WORDS  NAME is set to that element  and     the COMMANDS are executed  for     for    exp1  exp2  exp3     do COMMANDS  done     Equivalent to            EXP1            while    EXP2     do             COMMANDS                EXP3            done     EXP1  EXP2  and EXP3 are arithmetic expressions   If any expression is     omitted  it behaves as if it evaluates to 1

User · Answer

I commonly like to use a slight variant on the standard for loop   I often use this to run a command on a series of remote hosts   I take advantage of bash s brace expansion to create for loops that allow me to create non-numerical for-loops   Example   I want to run the uptime command on frontend hosts 1-5 and backend hosts 1-3     for host in  frontend 1  5  backend 1  3   mycompany com     do ssh  host  echo -n  host  uptime    done   I typically run this as a single-line command with semicolons on the ends of the lines instead of the more readable version above   The key usage consideration are that braces allow you to specify multiple values to be inserted into a string  e g  pre foo bar post results in prefoopost  prebarpost  and allow counting sequences by using the double periods  you can use a  z etc     However  the double period syntax is a new feature of bash 3 0  earlier versions will not support this

[bash] How do I write a for loop in bash

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