diff options
Diffstat (limited to 'bash.html.markdown')
| -rw-r--r-- | bash.html.markdown | 17 |
1 files changed, 13 insertions, 4 deletions
diff --git a/bash.html.markdown b/bash.html.markdown index d4f3d424..bd2d5984 100644 --- a/bash.html.markdown +++ b/bash.html.markdown @@ -83,24 +83,33 @@ echo Hello, $Name! # We have the usual if structure: # use 'man test' for more info about conditionals -if [ $Name -ne $USER ] +if [ $Name != $USER ] then echo "Your name isn't your username" else echo "Your name is your username" fi +# NOTE: if $Name is empty, bash sees the above condition as: +if [ != $USER ] +# which is invalid syntax +# so the "safe" way to use potentially empty variables in bash is: +if [ "$Name" != $USER ] ... +# which, when $Name is empty, is seen by bash as: +if [ "" != $USER ] ... +# which works as expected + # There is also conditional execution echo "Always executed" || echo "Only executed if first command fails" echo "Always executed" && echo "Only executed if first command does NOT fail" # To use && and || with if statements, you need multiple pairs of square brackets: -if [ $Name == "Steve" ] && [ $Age -eq 15 ] +if [ "$Name" == "Steve" ] && [ "$Age" -eq 15 ] then echo "This will run if $Name is Steve AND $Age is 15." fi -if [ $Name == "Daniya" ] || [ $Name == "Zach" ] +if [ "$Name" == "Daniya" ] || [ "$Name" == "Zach" ] then echo "This will run if $Name is Daniya OR Zach." fi @@ -252,7 +261,7 @@ grep "^foo.*bar$" file.txt grep -c "^foo.*bar$" file.txt # if you literally want to search for the string, # and not the regex, use fgrep (or grep -F) -fgrep "^foo.*bar$" file.txt +fgrep "^foo.*bar$" file.txt # Read Bash shell builtins documentation with the bash 'help' builtin: |