From f4022052471d6dc0a9c2fb8794e1352253b4c5ad Mon Sep 17 00:00:00 2001 From: Awal Garg Date: Wed, 14 Oct 2015 21:10:28 +0530 Subject: [bash/en] use $var with quotes in conditions --- bash.html.markdown | 13 +++++++++++-- 1 file changed, 11 insertions(+), 2 deletions(-) (limited to 'bash.html.markdown') diff --git a/bash.html.markdown b/bash.html.markdown index 191f916a..211d2944 100644 --- a/bash.html.markdown +++ b/bash.html.markdown @@ -90,17 +90,26 @@ else echo "Your name is your username" fi +# NOTE: if $Name is empty, bash sees the above condition as: +if [ -ne $USER ] +# which is invalid syntax +# so the "safe" way to use potentially empty variables in bash is: +if [ "$Name" -ne $USER ] ... +# which, when $Name is empty, is seen by bash as: +if [ "" -ne $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 -- cgit v1.2.3