If not quoted, it is a pattern match! (From the Bash man page: "Any part of the pattern may be quoted to force it to be matched as a string."). Here in Bash, the two statements yielding "yes" are pattern matching, other three are string equality:
Make sure you have the #!/bin/bash shebang line for your script if you use double brackets. See also Bash FAQ - "What is the difference between test, [ and [ [ ?" Bash Practices - Bash Tests Server Fault - What is the difference between double and single brackets in bash?
Modern shells such as Bash and Zsh have inherited this construct from Ksh, but it is not part of the POSIX specification. If you're in an environment where you have to be strictly POSIX compliant, stay away from it; otherwise, it's basically down to personal preference.
Bash always seemed backward with numeric evaluations using an operator consisting of a string (-eq) and string comparisons using a numeric operator "==" or "=" just you mess you up. If you ask me I'd say the problem is the distro swapping out bash. That is just my opinion, but this is my fix.
When writing shell programs, we often use /bin/sh and /bin/bash. I usually use bash, but I don't know what's the difference between them. What's the main difference between Bash and sh? What do we ...
Related discusions: bash for loop: a range of numbers and unix.stackexchange.com - In bash, is it possible to use an integer variable in the loop control of a for loop?
All the bash command line switches are documented in man bash. -e Exit immediately if a pipeline (which may consist of a single simple command), a subshell command enclosed in parentheses, or one of the commands executed as part of a command list enclosed by braces (see SHELL GRAMMAR above) exits with a non-zero status. The shell does not exit if the command that fails is part of the command ...
For example, FreeBSD doesn't ship with bash (it's installable from ports though). Scripts written assuming bash features aren't portable, and they're noticably slower slower than most Bourne shell implementations (like dash, which is common on GNU/Linux distributions). bash is a nice interactive shell, but it's slow for scripting.
#!/bin/bash # To focus exclusively on the performance of each type of increment # statement, we should exclude bash performing while loops from the # performance measure.
