Bash Error Handling Pipe
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Bash Pipe Error To File
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Bash Error Handling Best Practices
up catching error codes in a shell pipe up vote 52 down vote favorite 14 I currently have a script that does something like ./a | ./b | ./c I want to modify it so that if any of a, b or c exit with an error code I print an error message and stop instead of piping bad output forward. What would linux bash error handling be the simplest/cleanest way to do so? shell pipe share|improve this question asked Oct 11 '09 at 15:17 hugomg 41.8k985169 4 There really needs to be something like &&| which would mean "only continue the pipe if the preceding command was successful". I suppose you could also have ||| which would mean "continue the pipe if the preceding command failed" (and possibly pipe the error message like Bash 4's |&). –Dennis Williamson Oct 14 '09 at 7:28 2 @DennisWilliamson, you can't "stop the pipe" because a, b, c commands are not run sequentially but in parallel. In other words, data flows sequentially from a to c, but the actual a, b and c commands start (roughly) at the same time. –Giacomo Jun 4 '12 at 11:09 add a comment| 4 Answers 4 active oldest votes up vote 10 down vote accepted If you really don't want the second command to proceed until the first is known to be successful, then you probably need to use temporary files. The simple version of that is: tmp=${TMPDIR:-/tmp}/mine.$$ if ./a > $tmp.1 then if ./b <$tmp.1 >$tmp.2 t
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Error Handling In Bash Shell Script
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Bash Pipe Stderr
with us Stack Overflow Questions Jobs Documentation Tags Users Badges Ask Question x Dismiss Join the Stack Overflow Community Stack Overflow bash throw error is a community of 4.7 million programmers, just like you, helping each other. Join them; it only takes a minute: Sign up bash: pipe output AND capture exit status up vote 215 down vote favorite http://stackoverflow.com/questions/1550933/catching-error-codes-in-a-shell-pipe 57 I want to execute a long running command in bash shell, and both capture its exit status, and tee its output. So I do this command | tee out.txt ST=$? The problem is that the variable ST captures the exit status of tee and not of command. How can I solve this? Note that command is long running and redirecting the output to a file to view it http://stackoverflow.com/questions/1221833/bash-pipe-output-and-capture-exit-status later is not a good solution for me. linux bash shell redirect tee share|improve this question edited May 17 '13 at 15:17 lesmana 12.8k64469 asked Aug 3 '09 at 11:31 flybywire 64.3k145334456 [[ "${PIPESTATUS[@]}" =~ [^0\ ] ]] && echo -e "Match - error found" || echo -e "No match - all good" This will test all the values of the array at once and give an error message if any of the pipe values returned are not zero. This is a pretty robust generalized solution for detecting errors in a piped situation. –Brian S. Wilson Mar 31 '15 at 19:08 add a comment| 13 Answers 13 active oldest votes up vote 292 down vote accepted There is an internal Bash variable called $PIPESTATUS; it’s an array that holds the exit status of each command in your last foreground pipeline of commands.
when using it, whether interactively or in a script. This file attempts to describe some of them, demonstrate that they are indeed mistakes, and show how http://www.greenend.org.uk/rjk/tech/shellmistakes.html to avoid them. 0.1 Assumptions Basic familiarity with UNIX and Bourne shell is assumed: the reader will probably have written simple shell scripts already, and if not will at least know what the idea of a script is. This isn't a complete shell tutorial. 0.2 Typographical Conventions Examples are displayed boxed: Example In transcripts of shell sessions, user input is displayed specially, to distinguish it from error handling the output of the computer: sfere$ echo wibble wibble This will only work if your browser supports style sheets. The distinction between user input and computer output will usually be reasonably obvious from context, however. 1. Redundant cat It seems to be extremely common to use "cat" to feed input into some filter. For example: cat file | grep searchstring The effect of this is to bash error handling create a pipe, executing "cat file" with its output redirected to the pipe and "grep searchstring" with its input redirected from the pipe. But you can eliminate the entire invocation of "cat" by just redirecting grep's input to come from the file: grep searchstring < file Not only does this avoid the time-wasting invocation of "cat", but (depending on the program you are running) it can sometimes make the process more efficient still by giving the program more direct access to the file. (If performance is really vital than you should test the various possibilities rather than speculating that one is faster than another, though.) If what you want is to have the input file at the start rather than the end, you can do that too: < file grep searchstring In this case you can also just pass the name of the file to grep: grep searchstring file In other cases that might change the behaviour, though. 1.1 Exceptions Very occasionally it does make sense to put in the "cat": if the process that reads the input behaves differently depending on whether it is a regular file, a pipe, a terminal, etc, then it might