Emulating a do-while loop in Bash

Question

What is the best way to emulate a do-while loop in Bash   I could check for the condition before entering the while loop  and then continue re-checking the condition in the loop  but that s duplicated code  Is there a cleaner way   Pseudo code of my script   while   current time  lt    cutoff    do     check if file present      do other stuff done   This doesn t perform check if file present if launched after the  cutoff time  and a do-while would

User · Answer

This implementation   Has no code duplication Doesn t require extra functions   Doesn t depend on the return value of code in the  quot while quot  section of the loop     do true while  do    conditions  do   do false     your code     done  It works with a read loop  too  skipping the first read  do true while  do    read foo  do   do false      your code       echo  foo done

User · Answer

Two simple solutions    Execute your code once before the while loop  actions        check if file present      Do other stuff    actions  1st execution while   current time  lt    cutoff    do    actions   Loop execution done  Or   while     do     actions        current time  lt    cutoff       break done

User · Answer

We can emulate a do-while loop in Bash with while   condition    do true  done like this   while    current time  lt    cutoff        check if file present      do other stuff do true  done   For an example  Here is my implementation on getting ssh connection in bash script      bin bash while     STATUS    0        ssh-add -l  amp  gt  dev null  STATUS          if     STATUS    127     then echo  ssh not instaled   amp  amp  exit 0      elif     STATUS    2     then echo  running ssh-agent     amp  amp  eval  ssh-agent   gt   dev null      elif     STATUS    1     then echo  get session identity     amp  amp  expect  HOME agent  amp  gt   dev null      else ssh-add -l  amp  amp  git submodule update --init --recursive --remote --merge  amp  amp  return 0  fi do true  done   It will give the output in sequence as below   Step  0 -  gcloud   intalling expect   Step  0 -  gcloud   running ssh-agent   Step  0 -  gcloud   get session identity   Step  0 -  gcloud   4096 SHA256 XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX  builder home  ssh id rsa  RSA  Step  0 -  gcloud   Submodule   google cloud compute home chetabahana  docker compose   git github com chetabahana compose  registered for path   google cloud compute home chetabahana  docker compose  Step  0 -  gcloud   Cloning into   workspace  io  google cloud compute home chetabahana  docker compose     Step  0 -  gcloud   Warning  Permanently added the RSA host key for IP address  XXX XX XXX XXX  to the list of known hosts  Step  0 -  gcloud   Submodule path   google cloud compute home chetabahana  docker compose   checked out  24a28a7a306a671bbc430aa27b83c09cc5f1c62d  Finished Step  0 -  gcloud

User · Answer

Place the body of your loop after the while and before the test  The actual body of the while loop should be a no-op   while      check if file present      do other stuff        current time  lt   cutoff    do       done   Instead of the colon  you can use continue if you find that more readable  You can also insert a command that will only run between iterations  not before first or after last   such as echo  Retrying in five seconds   sleep 5  Or print delimiters between values   i 1  while printf   d      i          i  lt   4    do printf      done  printf   n    I changed the test to use double parentheses since you appear to be comparing integers  Inside double square brackets  comparison operators such as  lt   are lexical and will give the wrong result when comparing 2 and 10  for example  Those operators don t work inside single square brackets

[bash] Emulating a do-while loop in Bash

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