Shell script for loop syntax

Question

I have gotten the following to work   for i in  2  10  do     echo  output   i  done   It produces a bunch of lines of output  2  output  3  so on   However  trying to run the following   max 10 for i in  2   max  do     echo   i  done   produces the following   output   2  10    How can I get the compiler to realize it should treat  max as the other end of the array  and not part of a string

User · Answer

Try the arithmetic-expression version of for:

max=10
for (( i=2; i <= $max; ++i ))
do
    echo "$i"
done

This is available in most versions of bash, and should be Bourne shell (sh) compatible also.

User · Answer

Brace expansion   x  y  is performed before other expansions  so you cannot use that for variable length sequences   Instead  use the seq 2  max method as user mob stated   So  for your example it would be   max 10 for i in  seq 2  max  do     echo   i  done

User · Answer

These all do  1  8  and should all be POSIX  They also will not break if you put a conditional continue in the loop  The canonical way   f  while      f  1   -le 8   do   echo  f done   Another way   g  while   g   g 1        g  -le 8   do   echo    g  done   and another   set -- while   set               -le 8   do   echo      done

User · Answer

This is a way  Bash   max 10 for i in   bash -c  echo  2    max      do echo  i  done   The above Bash way will work for ksh and zsh too  when bash -c is replaced with ksh -c or zsh -c respectively   Note  for i in  2    max    do echo  i  done works in zsh and ksh

User · Answer

We can iterate loop like as C programming      bin bash for   i 1  i lt  20  i i 1   do        echo  i done

User · Answer

Step the loop manually    i 0 max 10 while    i -lt  max   do     echo  output   i      true     i      done   If you don   t have to be totally POSIX  you can use the arithmetic for loop    max 10 for    i 0  i  lt max  i       do echo  output   i   done   Or use jot 1  on BSD systems    for i in    jot 0 10    do echo  output   i   done

User · Answer

Here it worked on Mac nbsp OS nbsp X   It includes the example of a BSD date  how to increment and decrement the date also   for   i 28  i gt  6   i--    do     dat  date -v-  i d -j    Y m d        echo  dat done

User · Answer

If the seq command available on your system   for i in  seq 2  max  do   echo  output   i  done   If not  then use poor man s seq with perl   seq  perl -e          print 2   max   for i in  seq do   echo  output   i  done   Watch those quote marks

User · Answer

Use   max 10 for i in  eval echo  2   max   do     echo  i done   You need the explicit  eval  call to reevaluate the    after variable substitution

User · Answer

Well  as I didn t have the seq command installed on my system  Mac nbsp OS nbsp X nbsp v10 6 1  Snow nbsp Leopard    I ended up using a while loop instead   max 5 i 1  while    max -gt  i   do      stuff  done    Shrugs  Whatever works

User · Answer

There s more than one way to do it   max 10 for i in  eval  echo  2   max    do     echo   i  done

[unix] Shell script "for" loop syntax

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