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[Explore Stack Internal](https://stackoverflow.co/internal/?utm_medium=referral&utm_source=askubuntu-community&utm_campaign=side-bar&utm_content=explore-teams-compact-popover) # [for loop syntax in shell script \[duplicate\]](https://askubuntu.com/questions/621981/for-loop-syntax-in-shell-script) [Ask Question](https://askubuntu.com/questions/ask) Asked 10 years, 10 months ago Modified [10 years, 10 months ago](https://askubuntu.com/questions/621981/for-loop-syntax-in-shell-script?lastactivity "2015-05-10 21:32:50Z") Viewed 86k times This question shows research effort; it is useful and clear 8 Save this question. Show activity on this post. **This question already has answers here**: [What is the difference between ./ and sh to run a script?](https://askubuntu.com/questions/22910/what-is-the-difference-between-and-sh-to-run-a-script) (6 answers) Closed 10 years ago. I run below script: ``` for (( i=1; i <= 5; i++ )) do echo "Random number $i: $RANDOM" done ``` I am getting below Error: ``` Syntax error: Bad for loop variable ``` why this syntax is not working? - [scripts](https://askubuntu.com/questions/tagged/scripts "show questions tagged 'scripts'") [Share](https://askubuntu.com/q/621981 "Short permalink to this question") Share a link to this question Copy link [CC BY-SA 3.0](https://creativecommons.org/licenses/by-sa/3.0/ "The current license for this post: CC BY-SA 3.0") [Improve this question](https://askubuntu.com/posts/621981/edit) Follow Follow this question to receive notifications [edited May 10, 2015 at 19:31](https://askubuntu.com/posts/621981/revisions "show all edits to this post") [](https://askubuntu.com/users/367165/a-b) [A.B.](https://askubuntu.com/users/367165/a-b) 92\.5k2222 gold badges255255 silver badges330330 bronze badges asked May 10, 2015 at 18:12 [](https://askubuntu.com/users/398408/akshay-patel) [Akshay Patel](https://askubuntu.com/users/398408/akshay-patel) 34522 gold badges44 silver badges77 bronze badges 8 - When I copy-paste this into my terminal, it works as inteded. Do you have something else stored in `i` or have a file named "i" in your WD? s3lph – [s3lph](https://askubuntu.com/users/194948/s3lph "14,744 reputation") 2015-05-10 18:15:25 +00:00 [Commented May 10, 2015 at 18:15](https://askubuntu.com/questions/621981/for-loop-syntax-in-shell-script#comment880222_621981) - 1 You are probably running it in `sh` ..the syntax is correct for `bash` ..how are you running it? heemayl – [heemayl](https://askubuntu.com/users/216503/heemayl "94,477 reputation") 2015-05-10 18:15:58 +00:00 [Commented May 10, 2015 at 18:15](https://askubuntu.com/questions/621981/for-loop-syntax-in-shell-script#comment880223_621981) - 1 What command are you using to run the script? heemayl – [heemayl](https://askubuntu.com/users/216503/heemayl "94,477 reputation") 2015-05-10 18:19:25 +00:00 [Commented May 10, 2015 at 18:19](https://askubuntu.com/questions/621981/for-loop-syntax-in-shell-script#comment880227_621981) - 1 As far as your previous records are concerned, you should [read this](http://stackoverflow.com/help/someone-answers) heemayl – [heemayl](https://askubuntu.com/users/216503/heemayl "94,477 reputation") 2015-05-10 18:46:23 +00:00 [Commented May 10, 2015 at 18:46](https://askubuntu.com/questions/621981/for-loop-syntax-in-shell-script#comment880245_621981) - 1 You may be interested in an answer by a user posted on my question here: [unix.stackexchange.com/questions/198985/…](http://unix.stackexchange.com/questions/198985/how-to-make-mksh-for-loop-go-from-1-to-n "how to make mksh for loop go from 1 to n") Sergiy Kolodyazhnyy – [Sergiy Kolodyazhnyy](https://askubuntu.com/users/295286/sergiy-kolodyazhnyy "108,386 reputation") 2015-05-10 19:49:31 +00:00 [Commented May 10, 2015 at 19:49](https://askubuntu.com/questions/621981/for-loop-syntax-in-shell-script#comment880289_621981) \| [Show **3** more comments](https://askubuntu.com/questions/621981/for-loop-syntax-in-shell-script "Expand to show all comments on this post") ## 3 Answers 3 Sorted by: [Reset to default](https://askubuntu.com/questions/621981/for-loop-syntax-in-shell-script?answertab=scoredesc#tab-top) This answer is useful 14 Save this answer. Show activity on this post. As heemayl's answer points out, your construction is a bashism. The standard way of doing what you want would be: ``` for i in 1 2 3 4 5 do echo "Random number $i: $RANDOM" done ``` Or, more easily expandably: ``` for i in $(seq 1 5) do echo "Random number $i: $RANDOM" done ``` (See `man seq` for more detail). [Share](https://askubuntu.com/a/621986 "Short permalink to this answer") Share a link to this answer Copy link [CC BY-SA 3.0](https://creativecommons.org/licenses/by-sa/3.0/ "The current license for this post: CC BY-SA 3.0") [Improve this answer](https://askubuntu.com/posts/621986/edit) Follow Follow this answer to receive notifications [edited May 10, 2015 at 18:44](https://askubuntu.com/posts/621986/revisions "show all edits to this post") answered May 10, 2015 at 18:36 [](https://askubuntu.com/users/112879/evilsoup) [evilsoup](https://askubuntu.com/users/112879/evilsoup) 4,62511 gold badge2323 silver badges2626 bronze badges 6 - Brace expansion is also a bashism. muru – [muru](https://askubuntu.com/users/158442/muru "209,415 reputation") ♦ 2015-05-10 18:38:17 +00:00 [Commented May 10, 2015 at 18:38](https://askubuntu.com/questions/621981/for-loop-syntax-in-shell-script#comment880237_621986) - 1 `for i in 1 2 3 4 5` is kind of trolling....use `seq 1 5`.. heemayl – [heemayl](https://askubuntu.com/users/216503/heemayl "94,477 reputation") 2015-05-10 18:41:07 +00:00 [Commented May 10, 2015 at 18:41](https://askubuntu.com/questions/621981/for-loop-syntax-in-shell-script#comment880238_621986) - @heemayl -- Not trolling, I just had to double-check the seq syntax before I included it evilsoup – [evilsoup](https://askubuntu.com/users/112879/evilsoup "4,625 reputation") 2015-05-10 18:45:35 +00:00 [Commented May 10, 2015 at 18:45](https://askubuntu.com/questions/621981/for-loop-syntax-in-shell-script#comment880244_621986) - @heemayl no trolling, some users don't know all the minute details of shell scripting =) Sergiy Kolodyazhnyy – [Sergiy Kolodyazhnyy](https://askubuntu.com/users/295286/sergiy-kolodyazhnyy "108,386 reputation") 2015-05-10 19:48:33 +00:00 [Commented May 10, 2015 at 19:48](https://askubuntu.com/questions/621981/for-loop-syntax-in-shell-script#comment880286_621986) - 3 Not that one can say `seq` is all that standard either. It's not POSIX. muru – [muru](https://askubuntu.com/users/158442/muru "209,415 reputation") ♦ 2015-05-10 19:49:25 +00:00 [Commented May 10, 2015 at 19:49](https://askubuntu.com/questions/621981/for-loop-syntax-in-shell-script#comment880287_621986) \| [Show **1** more comment](https://askubuntu.com/questions/621981/for-loop-syntax-in-shell-script "Expand to show all comments on this post") This answer is useful 6 Save this answer. Show activity on this post. Your original script has a `(( i=1; i <= 5; i++ ))` construct in `for` loop which is a bashism and hence is not being understood by `dash`. In Ubuntu `sh` is a symbolic link to `dash`, so when you are running ``` sh ./script.sh ``` you are basically running ``` dash ./script.sh ``` As i mentioned earlier `dash` is not understanding the C-like `for` loop construct, it is showing the error. To run the script using `bash`, you can: - Run it as as an argument to `bash` e.g. `bash script.sh` (you don't need to make the script executable) - Make the script executable and from a `bash` shell run (from the directory containing the script): ``` ./script.sh ``` - The most portable way is to use a shebang (`#!/bin/bash` or preferably `#!/usr/bin/env bash`) as the first line of your script. In this way you can run the script from any shell by `./script.sh`, the script will be interpreted as a `bash` script and hence will be executed accordingly. [Share](https://askubuntu.com/a/621983 "Short permalink to this answer") Share a link to this answer Copy link [CC BY-SA 3.0](https://creativecommons.org/licenses/by-sa/3.0/ "The current license for this post: CC BY-SA 3.0") [Improve this answer](https://askubuntu.com/posts/621983/edit) Follow Follow this answer to receive notifications [edited May 10, 2015 at 21:32](https://askubuntu.com/posts/621983/revisions "show all edits to this post") answered May 10, 2015 at 18:25 [](https://askubuntu.com/users/216503/heemayl) [heemayl](https://askubuntu.com/users/216503/heemayl) 94\.5k2323 gold badges216216 silver badges278278 bronze badges 2 - For even greater portability, a bash script can start with `#!/usr/bin/env bash`. Although not 100% of Unix-like systems have `env` in `/usr/bin`, those that don't are rarer than those with `bash` not in `bin`. (`bin` doesn't have `bash` on most systems where `bash` is installed but not part of the base system, e.g., FreeBSD.) Eliah Kagan – [Eliah Kagan](https://askubuntu.com/users/22949/eliah-kagan "120,140 reputation") 2015-05-10 21:16:01 +00:00 [Commented May 10, 2015 at 21:16](https://askubuntu.com/questions/621981/for-loop-syntax-in-shell-script#comment880341_621983) - @EliahKagan Yes..i forgot to mention `env`..that will be most portable.. heemayl – [heemayl](https://askubuntu.com/users/216503/heemayl "94,477 reputation") 2015-05-10 21:29:09 +00:00 [Commented May 10, 2015 at 21:29](https://askubuntu.com/questions/621981/for-loop-syntax-in-shell-script#comment880353_621983) [Add a comment](https://askubuntu.com/questions/621981/for-loop-syntax-in-shell-script "Use comments to ask for more information or suggest improvements. Avoid comments like “+1” or “thanks”.") \| This answer is useful 5 Save this answer. Show activity on this post. Thought I'd contribute to the discussion a little bit. It's already been mentioned that the syntax used in your script is a bashism and hence isn't portable, even though this is C-like and is well understood by those familiar with java and C. From asking my own [question](https://unix.stackexchange.com/q/198985/85039) on unix.stackexchange.com , I've also learned that syntax such as `for i in $(seq 1 5)` generates a set of numbers first and then iterates , which can be wasteful if you have a very large set. A better way to simulate C-like behavior, which is portable, is to use `while` loop, with a variable that can be incremented. For instance, ``` #!/bin/sh number=0 while [ "$number" -lt 10 ] do printf "\t%d" "$number" number=`expr $number + 1 ` done ``` This works with bash, dash, zsh, ksh, mksh . . . or basically any shell related to bourne shell. In fact, I've a Unix System V book from like 1995, and I've tested their example for bourne shell and it still works. The behaviour is also that of C-like for loop: you have initial condition, testing condition within `while [ . . .]`, and update condition at the end. [csh and tcsh](http://www.cyberciti.biz/faq/csh-shell-scripting-loop-example/) have syntax closer to C language, but its not portable to other shells, and they're [not recommended](http://www.grymoire.com/unix/CshTop10.txt) to be used in scripting. **Addition**: Concerning portability of \$RANDOM, according to [this page](https://wiki.ubuntu.com/DashAsBinSh#A.24RANDOM) on ubuntu wiki, with dash random number generation should rely on using `/dev/urandom` [Share](https://askubuntu.com/a/622034 "Short permalink to this answer") Share a link to this answer Copy link [CC BY-SA 3.0](https://creativecommons.org/licenses/by-sa/3.0/ "The current license for this post: CC BY-SA 3.0") [Improve this answer](https://askubuntu.com/posts/622034/edit) Follow Follow this answer to receive notifications [edited Apr 13, 2017 at 12:37](https://askubuntu.com/posts/622034/revisions "show all edits to this post") [](https://askubuntu.com/users/-1/community) [Community](https://askubuntu.com/users/-1/community)Bot 1 answered May 10, 2015 at 20:35 [](https://askubuntu.com/users/295286/sergiy-kolodyazhnyy) [Sergiy Kolodyazhnyy](https://askubuntu.com/users/295286/sergiy-kolodyazhnyy) 108k2121 gold badges295295 silver badges528528 bronze badges 1 - 1 This is indeed much more efficient when the loop variable can take on many values. For example, on my system, using `command time -f '%E' dash -c '...'` as the test harness, `for i in $(seq 1 100000000); do test $i -eq 1000 && break; done` took 0:48.37, but `i=1; while [ $i -lt 100000000 ]; do test $i -eq 1000 && break; i=$(expr $i + 1); done` took 0:02.23. Eliah Kagan – [Eliah Kagan](https://askubuntu.com/users/22949/eliah-kagan "120,140 reputation") 2015-05-10 21:13:01 +00:00 [Commented May 10, 2015 at 21:13](https://askubuntu.com/questions/621981/for-loop-syntax-in-shell-script#comment880337_622034) [Add a comment](https://askubuntu.com/questions/621981/for-loop-syntax-in-shell-script "Use comments to ask for more information or suggest improvements. Avoid comments like “+1” or “thanks”.") \| Start asking to get answers Find the answer to your question by asking. 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Thought I'd contribute to the discussion a little bit. It's already been mentioned that the syntax used in your script is a bashism and hence isn't portable, even though this is C-like and is well understood by those familiar with java and C. From asking my own [question](https://unix.stackexchange.com/q/198985/85039) on unix.stackexchange.com , I've also learned that syntax such as `for i in $(seq 1 5)` generates a set of numbers first and then iterates , which can be wasteful if you have a very large set. A better way to simulate C-like behavior, which is portable, is to use `while` loop, with a variable that can be incremented. For instance, ``` #!/bin/sh number=0 while [ "$number" -lt 10 ] do printf "\t%d" "$number" number=`expr $number + 1 ` done ``` This works with bash, dash, zsh, ksh, mksh . . . or basically any shell related to bourne shell. In fact, I've a Unix System V book from like 1995, and I've tested their example for bourne shell and it still works. The behaviour is also that of C-like for loop: you have initial condition, testing condition within `while [ . . .]`, and update condition at the end. [csh and tcsh](http://www.cyberciti.biz/faq/csh-shell-scripting-loop-example/) have syntax closer to C language, but its not portable to other shells, and they're [not recommended](http://www.grymoire.com/unix/CshTop10.txt) to be used in scripting. **Addition**: Concerning portability of \$RANDOM, according to [this page](https://wiki.ubuntu.com/DashAsBinSh#A.24RANDOM) on ubuntu wiki, with dash random number generation should rely on using `/dev/urandom`