Bash is Testing
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The document discusses the use of bash commands and their return values, including handling success and failure in scripts. It explains the syntax of conditional statements and the use of boolean operators such as && and ||. Additionally, the text highlights the readability of code and provides examples of common command usage in bash.
![Bash is Testing @mt165pro
$ which true
/bin/true
# true: “does nothing, successfully” [man(1) true, 1991]
$ file /bin/true
/bin/true: ELF 64-bit LSB shared object, x86-64, version 1 (SYSV),
dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, for
GNU/Linux 3.2.0, BuildID[sha1]=cae1cea2c8b5f2d151aceb44bcbe1d8415bc06c5,
stripped
7](https://image.slidesharecdn.com/bashistesting-devopsdaysldn20181-180925085236/85/Bash-is-Testing-7-320.jpg)
![Bash is Testing @mt165pro
# you may have seen script like this:
$ if [ “a” == “b” ]; then echo “hello”; fi
10](https://image.slidesharecdn.com/bashistesting-devopsdaysldn20181-180925085236/85/Bash-is-Testing-10-320.jpg)
![Bash is Testing @mt165pro
$ if [ -x foo ]; then echo “yes”; fi
# /usr/bin/[ is the command
# its arguments are: -x, foo, … and ]
13](https://image.slidesharecdn.com/bashistesting-devopsdaysldn20181-180925085236/85/Bash-is-Testing-12-320.jpg)
![Bash is Testing @mt165pro
# what does this print?
$ if [ a && b ]; then echo “yes”; else echo “no”; fi
no
16](https://image.slidesharecdn.com/bashistesting-devopsdaysldn20181-180925085236/85/Bash-is-Testing-13-320.jpg)
![Bash is Testing @mt165pro
# what about this one?
$ if [ false ]; then echo “yes”; else echo “no”; fi
yes
18](https://image.slidesharecdn.com/bashistesting-devopsdaysldn20181-180925085236/85/Bash-is-Testing-15-320.jpg)
![Bash is Testing @mt165pro
# what about this one?
$ if [ false ]; then echo “yes”; else echo “no”; fi
yes
19](https://image.slidesharecdn.com/bashistesting-devopsdaysldn20181-180925085236/85/Bash-is-Testing-16-320.jpg)
![Bash is Testing @mt165pro
# syntaces can be combined
$ if [ -n “$foo” -a -f bar ] && which baz; then echo “yes”; fi
# but remember that code’s primary purpose is to be read...
20](https://image.slidesharecdn.com/bashistesting-devopsdaysldn20181-180925085236/85/Bash-is-Testing-17-320.jpg)
![Bash is Testing @mt165pro
# turns out, && and || are short-cct
$ if true || rm -rf /; then echo “you’re fine”; fi
# no if statement required
$ grep “needle” haystack && echo “found it”
# commonly used with /bin/[
$ [ -x foo ] && ./foo
# || even binds less tightly
$ [ -x foo ] && ./foo || echo “foo not executable”
# yay BODMAS
21](https://image.slidesharecdn.com/bashistesting-devopsdaysldn20181-180925085236/85/Bash-is-Testing-18-320.jpg)
![Bash is Testing @mt165pro
# turns out, && and || are short-cct
$ if true || rm -rf /; then echo “you’re fine”; fi
# no if statement required
$ grep “needle” haystack && echo “found it”
# commonly used with /bin/[
$ [ -x foo ] && ./foo
# || even binds less tightly
$ [ -x foo ] && ./foo || echo “foo not executable”
# yay BODMAS
22](https://image.slidesharecdn.com/bashistesting-devopsdaysldn20181-180925085236/85/Bash-is-Testing-19-320.jpg)
Bash is Testing
- 1. Bash is Testing @mt165pro Testing in Bash Matt Turner @mt165pro mt165.co.uk DevOps Days London September 2018 aka Bash is Testing
- 2. Bash is Testing @mt165pro # A command has has a stdout, a stderr, and an exit code 2
- 3. Bash is Testing @mt165pro # All commands have a return value # No matter what they write to stdout or stderr $ ls foo bar $ echo $? 0 3
- 4. Bash is Testing @mt165pro # Usually commands succeed # Even when they don’t, you often don’t care $ grep “needle” haystack grep: haystack: No such file or directory $ echo $? 2 4
- 5. Bash is Testing @mt165pro # How do you test success / failure in a script? $ if true; then echo “yes”; else echo “no”; fi yes 5
- 6. Bash is Testing @mt165pro # if is a piece of bash syntax # it “takes precisely one argument: a command that returns 0 or non-0” # … a command that returns 0 or non-0 6
- 7. Bash is Testing @mt165pro $ which true /bin/true # true: “does nothing, successfully” [man(1) true, 1991] $ file /bin/true /bin/true: ELF 64-bit LSB shared object, x86-64, version 1 (SYSV), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, for GNU/Linux 3.2.0, BuildID[sha1]=cae1cea2c8b5f2d151aceb44bcbe1d8415bc06c5, stripped 7
- 8. Bash is Testing @mt165pro $ if which flibble; then echo “yes”; echo echo “no” fi No # which is a command. A unary one $ which which /usr/bin/which 8
- 9. Bash is Testing @mt165pro # These commands can be combined with boolean operators # which are part of the bash syntax # they are: ! && || $ if which foo || which bar; then echo “yes”; fi 9
- 10. Bash is Testing @mt165pro # you may have seen script like this: $ if [ “a” == “b” ]; then echo “hello”; fi 10
- 11. Bash is Testing @mt165pro $ which [ /usr/bin/[ 11
- 12. Bash is Testing @mt165pro $ if [ -x foo ]; then echo “yes”; fi # /usr/bin/[ is the command # its arguments are: -x, foo, … and ] 13
- 13. Bash is Testing @mt165pro # what does this print? $ if [ a && b ]; then echo “yes”; else echo “no”; fi no 16
- 14. Bash is Testing @mt165pro # what does this print? $ if true -a ls; then echo “yes”; else echo “no”; fi yes 17
- 15. Bash is Testing @mt165pro # what about this one? $ if [ false ]; then echo “yes”; else echo “no”; fi yes 18
- 16. Bash is Testing @mt165pro # what about this one? $ if [ false ]; then echo “yes”; else echo “no”; fi yes 19
- 17. Bash is Testing @mt165pro # syntaces can be combined $ if [ -n “$foo” -a -f bar ] && which baz; then echo “yes”; fi # but remember that code’s primary purpose is to be read... 20
- 18. Bash is Testing @mt165pro # turns out, && and || are short-cct $ if true || rm -rf /; then echo “you’re fine”; fi # no if statement required $ grep “needle” haystack && echo “found it” # commonly used with /bin/[ $ [ -x foo ] && ./foo # || even binds less tightly $ [ -x foo ] && ./foo || echo “foo not executable” # yay BODMAS 21
- 19. Bash is Testing @mt165pro # turns out, && and || are short-cct $ if true || rm -rf /; then echo “you’re fine”; fi # no if statement required $ grep “needle” haystack && echo “found it” # commonly used with /bin/[ $ [ -x foo ] && ./foo # || even binds less tightly $ [ -x foo ] && ./foo || echo “foo not executable” # yay BODMAS 22
- 20. Bash is Testing @mt165pro Bash is Testing 26