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How to repeat loop n times in Bash

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6

I have below scenario like:

if [file exists]; then
 exit 
elif
 recheck if file exist (max 10 times)
 if found exit else recheck again as per counter 
fi 

bash shell-script

share|improve this question

edited 20 mins ago

Rui F Ribeiro

41.3k1481140

asked Aug 5 '18 at 6:31

Rocky86Rocky86

7119

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  This is a very basic feature in shells. Did you even research it?
  
  – Peschke
  Aug 5 '18 at 7:03
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Yes. But not getting expected output from my code. Also want to write as abbreviated as possible
  
  – Rocky86
  Aug 5 '18 at 7:05
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  @Peschke, well, they'd need at least what, three basic features (loops, conditionals, testing the file, breaking out of a loop). At least the question is quite clear as it is. Though it could contain a sketch of what Rocky tried, but then someone would rewrite it full in the answers anyway. ;)
  
  – ilkkachu
  Aug 5 '18 at 7:07
  

  
  
  
  

add a comment | 

6

I have below scenario like:

if [file exists]; then
 exit 
elif
 recheck if file exist (max 10 times)
 if found exit else recheck again as per counter 
fi 

bash shell-script

share|improve this question

edited 20 mins ago

Rui F Ribeiro

41.3k1481140

asked Aug 5 '18 at 6:31

Rocky86Rocky86

7119

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  This is a very basic feature in shells. Did you even research it?
  
  – Peschke
  Aug 5 '18 at 7:03
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Yes. But not getting expected output from my code. Also want to write as abbreviated as possible
  
  – Rocky86
  Aug 5 '18 at 7:05
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  @Peschke, well, they'd need at least what, three basic features (loops, conditionals, testing the file, breaking out of a loop). At least the question is quite clear as it is. Though it could contain a sketch of what Rocky tried, but then someone would rewrite it full in the answers anyway. ;)
  
  – ilkkachu
  Aug 5 '18 at 7:07
  

  
  
  
  

add a comment | 

I have below scenario like:

if [file exists]; then
 exit 
elif
 recheck if file exist (max 10 times)
 if found exit else recheck again as per counter 
fi 

bash shell-script

share|improve this question

edited 20 mins ago

Rui F Ribeiro

41.3k1481140

asked Aug 5 '18 at 6:31

Rocky86Rocky86

7119

if [file exists]; then
 exit 
elif
 recheck if file exist (max 10 times)
 if found exit else recheck again as per counter 
fi 

share|improve this question

edited 20 mins ago

Rui F Ribeiro

41.3k1481140

asked Aug 5 '18 at 6:31

Rocky86Rocky86

7119

share|improve this question

edited 20 mins ago

Rui F Ribeiro

41.3k1481140

asked Aug 5 '18 at 6:31

Rocky86Rocky86

7119

edited 20 mins ago

Rui F Ribeiro

41.3k1481140

edited 20 mins ago

Rui F Ribeiro

41.3k1481140

asked Aug 5 '18 at 6:31

Rocky86Rocky86

7119

asked Aug 5 '18 at 6:31

Rocky86Rocky86

7119

3 Answers
3

active

oldest

votes

7

There are many ways to do this loop.

With ksh93 syntax (also supported by zsh and bash):

for (( i=0; i<10; ++i)); do
 [ -e filename ] && break
 sleep 10
done

For any POSIX-like shell:

n=0
while [ "$n" -lt 10 ] && [ ! -e filename ]; do
 n=$(( n + 1 ))
 sleep 10
done

Both of the loops sleep 10 seconds in each iteration before testing the existence of the file again.

After the loop has finished, you will have to test for existence of the file a last time to figure out whether the loop exited due to running 10 times or due to the file appearing.

If you wish, and if you have access to inotify-tools, you may replace the sleep 10 call with

inotifywait -q -t 10 -e create ./ >/dev/null

This would wait for a file creation event to occur in the current directory, but would time out after 10 seconds. This way your loop would exit as soon as the given filename appeared (if it appeared).

The full code, with inotifywait (replace with sleep 10 if you don't want that), may look like

for (( i=0; i<10; ++i)); do
 [ -e filename ] && break
 inotifywait -q -t 10 -e create ./ >/dev/null
done

if [ -e filename ]; then
 echo 'file appeared!'
else
 echo 'file did not turn up in time'
fi

share|improve this answer

edited Aug 5 '18 at 7:54

answered Aug 5 '18 at 6:37

KusalanandaKusalananda

134k17255418

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  With inotify, you could almost replace the whole loop. Just test if the file is there, and if not, inotifywait for a 100 seconds. Almost, since the file could be created just between the test and the inotify, and you'd sleep for the full 100 seconds before timing out...
  
  – ilkkachu
  Aug 5 '18 at 7:12
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  @ilkkachu Yes, that's a good idea, but here I'm just using inotifywait as a drop-in replacement for sleep.
  
  – Kusalananda
  Aug 5 '18 at 7:15
  

  
  
  
  

add a comment | 

3

If the count is not a variable you can use brace expansion:

for i in 1..10 # you can also use 0..9
do
 whatever
done

If the count is a variable you can use the seq command:

count=10
for i in $(seq $count)
do
 whatever
done

share|improve this answer

answered Aug 5 '18 at 6:47

xenoidxenoid

3,1601725

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  I want to loop only if file is not found (max. 10 times). If found lets say 3rd time then exit successfully
  
  – Rocky86
  Aug 5 '18 at 6:49
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @Rocky86 : This does not contradict the solution proposed by xenoid. Nobody forces you to count until the end ....
  
  – user1934428
  Aug 6 '18 at 9:46
  

  
  
  
  

add a comment | 

0

n=0
until [ "$((n+=1))" -gt 10 ]
do <exists? command exit
done
echo oh noes!

though test -e file && exit is more flexible

share|improve this answer

answered Aug 5 '18 at 6:36

mikeservmikeserv

45.8k668160

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Why the question mark? Note that the behaviour for globs in the target of redirections varies between shells.
  
  – Stéphane Chazelas
  Aug 5 '18 at 6:57
  

  
  
  
  


• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  
  Note that it has the side effect of opening the file, which for fifos for instance can be quite bad (worse with a symlink to /dev/watchdog on Linux for instance)
  
  – Stéphane Chazelas
  Aug 5 '18 at 6:58
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Even in Bash, where this would look for a file like exists1 or such, it still prints a bunch of errors if/when a matching file isn't found. (Also it errors if there are multiple matches.) Any other shell I tested seems to give errors in any case...
  
  – ilkkachu
  Aug 5 '18 at 7:01
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @ikkachu - yeah. that was kinda the point. if the error happens, the script reports. if stderr should be suppressed, suppress it done 2<>/dev/null. does bash does that scripted? i thought it only effed that up in an -interactive context. still, exists? is as much as a filler name as file. but yeah, i hate quoting in redirects - if screws so much up.
  
  – mikeserv
  Aug 5 '18 at 7:19
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @Stéphane - no reason, really. but yeah, fifos, unreadables... thats why i noted test -e.
  
  – mikeserv
  Aug 5 '18 at 7:22
  

  
  
  
  

 | 
show 3 more comments

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7

There are many ways to do this loop.

With ksh93 syntax (also supported by zsh and bash):

for (( i=0; i<10; ++i)); do
 [ -e filename ] && break
 sleep 10
done

For any POSIX-like shell:

n=0
while [ "$n" -lt 10 ] && [ ! -e filename ]; do
 n=$(( n + 1 ))
 sleep 10
done

Both of the loops sleep 10 seconds in each iteration before testing the existence of the file again.

After the loop has finished, you will have to test for existence of the file a last time to figure out whether the loop exited due to running 10 times or due to the file appearing.

If you wish, and if you have access to inotify-tools, you may replace the sleep 10 call with

inotifywait -q -t 10 -e create ./ >/dev/null

This would wait for a file creation event to occur in the current directory, but would time out after 10 seconds. This way your loop would exit as soon as the given filename appeared (if it appeared).

The full code, with inotifywait (replace with sleep 10 if you don't want that), may look like

for (( i=0; i<10; ++i)); do
 [ -e filename ] && break
 inotifywait -q -t 10 -e create ./ >/dev/null
done

if [ -e filename ]; then
 echo 'file appeared!'
else
 echo 'file did not turn up in time'
fi

share|improve this answer

edited Aug 5 '18 at 7:54

answered Aug 5 '18 at 6:37

KusalanandaKusalananda

134k17255418

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  With inotify, you could almost replace the whole loop. Just test if the file is there, and if not, inotifywait for a 100 seconds. Almost, since the file could be created just between the test and the inotify, and you'd sleep for the full 100 seconds before timing out...
  
  – ilkkachu
  Aug 5 '18 at 7:12
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  @ilkkachu Yes, that's a good idea, but here I'm just using inotifywait as a drop-in replacement for sleep.
  
  – Kusalananda
  Aug 5 '18 at 7:15
  

  
  
  
  

add a comment | 

7

There are many ways to do this loop.

With ksh93 syntax (also supported by zsh and bash):

for (( i=0; i<10; ++i)); do
 [ -e filename ] && break
 sleep 10
done

For any POSIX-like shell:

n=0
while [ "$n" -lt 10 ] && [ ! -e filename ]; do
 n=$(( n + 1 ))
 sleep 10
done

Both of the loops sleep 10 seconds in each iteration before testing the existence of the file again.

After the loop has finished, you will have to test for existence of the file a last time to figure out whether the loop exited due to running 10 times or due to the file appearing.

If you wish, and if you have access to inotify-tools, you may replace the sleep 10 call with

inotifywait -q -t 10 -e create ./ >/dev/null

This would wait for a file creation event to occur in the current directory, but would time out after 10 seconds. This way your loop would exit as soon as the given filename appeared (if it appeared).

The full code, with inotifywait (replace with sleep 10 if you don't want that), may look like

for (( i=0; i<10; ++i)); do
 [ -e filename ] && break
 inotifywait -q -t 10 -e create ./ >/dev/null
done

if [ -e filename ]; then
 echo 'file appeared!'
else
 echo 'file did not turn up in time'
fi

share|improve this answer

edited Aug 5 '18 at 7:54

answered Aug 5 '18 at 6:37

KusalanandaKusalananda

134k17255418

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  With inotify, you could almost replace the whole loop. Just test if the file is there, and if not, inotifywait for a 100 seconds. Almost, since the file could be created just between the test and the inotify, and you'd sleep for the full 100 seconds before timing out...
  
  – ilkkachu
  Aug 5 '18 at 7:12
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  @ilkkachu Yes, that's a good idea, but here I'm just using inotifywait as a drop-in replacement for sleep.
  
  – Kusalananda
  Aug 5 '18 at 7:15
  

  
  
  
  

add a comment | 

There are many ways to do this loop.

With ksh93 syntax (also supported by zsh and bash):

for (( i=0; i<10; ++i)); do
 [ -e filename ] && break
 sleep 10
done

For any POSIX-like shell:

n=0
while [ "$n" -lt 10 ] && [ ! -e filename ]; do
 n=$(( n + 1 ))
 sleep 10
done

Both of the loops sleep 10 seconds in each iteration before testing the existence of the file again.

After the loop has finished, you will have to test for existence of the file a last time to figure out whether the loop exited due to running 10 times or due to the file appearing.

If you wish, and if you have access to inotify-tools, you may replace the sleep 10 call with

inotifywait -q -t 10 -e create ./ >/dev/null

This would wait for a file creation event to occur in the current directory, but would time out after 10 seconds. This way your loop would exit as soon as the given filename appeared (if it appeared).

The full code, with inotifywait (replace with sleep 10 if you don't want that), may look like

for (( i=0; i<10; ++i)); do
 [ -e filename ] && break
 inotifywait -q -t 10 -e create ./ >/dev/null
done

if [ -e filename ]; then
 echo 'file appeared!'
else
 echo 'file did not turn up in time'
fi

share|improve this answer

edited Aug 5 '18 at 7:54

answered Aug 5 '18 at 6:37

KusalanandaKusalananda

134k17255418

for (( i=0; i<10; ++i)); do
 [ -e filename ] && break
 sleep 10
done

n=0
while [ "$n" -lt 10 ] && [ ! -e filename ]; do
 n=$(( n + 1 ))
 sleep 10
done

inotifywait -q -t 10 -e create ./ >/dev/null

for (( i=0; i<10; ++i)); do
 [ -e filename ] && break
 inotifywait -q -t 10 -e create ./ >/dev/null
done

if [ -e filename ]; then
 echo 'file appeared!'
else
 echo 'file did not turn up in time'
fi

share|improve this answer

edited Aug 5 '18 at 7:54

answered Aug 5 '18 at 6:37

KusalanandaKusalananda

134k17255418

answered Aug 5 '18 at 6:37

KusalanandaKusalananda

134k17255418

answered Aug 5 '18 at 6:37

KusalanandaKusalananda

134k17255418

3

If the count is not a variable you can use brace expansion:

for i in 1..10 # you can also use 0..9
do
 whatever
done

If the count is a variable you can use the seq command:

count=10
for i in $(seq $count)
do
 whatever
done

share|improve this answer

answered Aug 5 '18 at 6:47

xenoidxenoid

3,1601725

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  I want to loop only if file is not found (max. 10 times). If found lets say 3rd time then exit successfully
  
  – Rocky86
  Aug 5 '18 at 6:49
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @Rocky86 : This does not contradict the solution proposed by xenoid. Nobody forces you to count until the end ....
  
  – user1934428
  Aug 6 '18 at 9:46
  

  
  
  
  

add a comment | 

3

If the count is not a variable you can use brace expansion:

for i in 1..10 # you can also use 0..9
do
 whatever
done

If the count is a variable you can use the seq command:

count=10
for i in $(seq $count)
do
 whatever
done

share|improve this answer

answered Aug 5 '18 at 6:47

xenoidxenoid

3,1601725

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  I want to loop only if file is not found (max. 10 times). If found lets say 3rd time then exit successfully
  
  – Rocky86
  Aug 5 '18 at 6:49
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @Rocky86 : This does not contradict the solution proposed by xenoid. Nobody forces you to count until the end ....
  
  – user1934428
  Aug 6 '18 at 9:46
  

  
  
  
  

add a comment | 

If the count is not a variable you can use brace expansion:

for i in 1..10 # you can also use 0..9
do
 whatever
done

If the count is a variable you can use the seq command:

count=10
for i in $(seq $count)
do
 whatever
done

share|improve this answer

answered Aug 5 '18 at 6:47

xenoidxenoid

3,1601725

for i in 1..10 # you can also use 0..9
do
 whatever
done

count=10
for i in $(seq $count)
do
 whatever
done

share|improve this answer

answered Aug 5 '18 at 6:47

xenoidxenoid

3,1601725

answered Aug 5 '18 at 6:47

xenoidxenoid

3,1601725

answered Aug 5 '18 at 6:47

xenoidxenoid

3,1601725

0

n=0
until [ "$((n+=1))" -gt 10 ]
do <exists? command exit
done
echo oh noes!

though test -e file && exit is more flexible

share|improve this answer

answered Aug 5 '18 at 6:36

mikeservmikeserv

45.8k668160

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Why the question mark? Note that the behaviour for globs in the target of redirections varies between shells.
  
  – Stéphane Chazelas
  Aug 5 '18 at 6:57
  

  
  
  
  


• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  
  Note that it has the side effect of opening the file, which for fifos for instance can be quite bad (worse with a symlink to /dev/watchdog on Linux for instance)
  
  – Stéphane Chazelas
  Aug 5 '18 at 6:58
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Even in Bash, where this would look for a file like exists1 or such, it still prints a bunch of errors if/when a matching file isn't found. (Also it errors if there are multiple matches.) Any other shell I tested seems to give errors in any case...
  
  – ilkkachu
  Aug 5 '18 at 7:01
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @ikkachu - yeah. that was kinda the point. if the error happens, the script reports. if stderr should be suppressed, suppress it done 2<>/dev/null. does bash does that scripted? i thought it only effed that up in an -interactive context. still, exists? is as much as a filler name as file. but yeah, i hate quoting in redirects - if screws so much up.
  
  – mikeserv
  Aug 5 '18 at 7:19
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @Stéphane - no reason, really. but yeah, fifos, unreadables... thats why i noted test -e.
  
  – mikeserv
  Aug 5 '18 at 7:22
  

  
  
  
  

 | 
show 3 more comments

0

n=0
until [ "$((n+=1))" -gt 10 ]
do <exists? command exit
done
echo oh noes!

though test -e file && exit is more flexible

share|improve this answer

answered Aug 5 '18 at 6:36

mikeservmikeserv

45.8k668160

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Why the question mark? Note that the behaviour for globs in the target of redirections varies between shells.
  
  – Stéphane Chazelas
  Aug 5 '18 at 6:57
  

  
  
  
  


• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  
  Note that it has the side effect of opening the file, which for fifos for instance can be quite bad (worse with a symlink to /dev/watchdog on Linux for instance)
  
  – Stéphane Chazelas
  Aug 5 '18 at 6:58
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Even in Bash, where this would look for a file like exists1 or such, it still prints a bunch of errors if/when a matching file isn't found. (Also it errors if there are multiple matches.) Any other shell I tested seems to give errors in any case...
  
  – ilkkachu
  Aug 5 '18 at 7:01
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @ikkachu - yeah. that was kinda the point. if the error happens, the script reports. if stderr should be suppressed, suppress it done 2<>/dev/null. does bash does that scripted? i thought it only effed that up in an -interactive context. still, exists? is as much as a filler name as file. but yeah, i hate quoting in redirects - if screws so much up.
  
  – mikeserv
  Aug 5 '18 at 7:19
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @Stéphane - no reason, really. but yeah, fifos, unreadables... thats why i noted test -e.
  
  – mikeserv
  Aug 5 '18 at 7:22
  

  
  
  
  

 | 
show 3 more comments

n=0
until [ "$((n+=1))" -gt 10 ]
do <exists? command exit
done
echo oh noes!

though test -e file && exit is more flexible

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answered Aug 5 '18 at 6:36

mikeservmikeserv

45.8k668160

n=0
until [ "$((n+=1))" -gt 10 ]
do <exists? command exit
done
echo oh noes!

share|improve this answer

answered Aug 5 '18 at 6:36

mikeservmikeserv

45.8k668160

answered Aug 5 '18 at 6:36

mikeservmikeserv

45.8k668160

answered Aug 5 '18 at 6:36

mikeservmikeserv

45.8k668160