Difference between "./" and "sh" in UNIX
sh file executes a shell-script file in a new shell process.
. file executes a shell-script file in the current shell process.
./file will execute the file in the current directory. The file can be a binary executable, or it can start with a hashbang line (the first line of the file in form of
#!...., for example
#!/usr/bin/ruby in a file would signify the script needs to be executed as a Ruby file). The file needs to have the executable flag set.
For example, if you have the script
and you execute it with
sh test.sh, you'd launch a new
sh (or rather
bash, most likely, as one is softlinked to the other in modern systems), then define a new variable inside it, then exit. A subsequent
echo $TEST prints an empty line - the variable is not set in the outer shell.
If you launch it using
. test.sh, you'd execute the script using the current shell. The result of
echo $TEST would print
If you launch it using
./test.sh, the first line
#!/bin/sh would be detected, then it would be exactly as if you wrote
/bin/sh ./test.sh, which in this case boils down to the first scenario. But if the hashbang line was, for example,
#!/usr/bin/perl -w, the file would have been executed with
/usr/bin/perl -w ./test.sh.
With sh , we can run a script that doesn’t have execute permission set on it, we run it as argument for sh, but ./ needs the permission as it is supposed to be an executable. In both cases, new shell will be created to run the script. See the below example:
[email protected]:~/shell# vi test1.sh #!/bin/bash my_var=hello echo $my_var #Shows the current shell processid echo $$ [email protected]:~/shell# echo $$ 1896 [email protected]:~/shell# sh test1.sh hello 2093 [email protected]:~/shell# ./test1.sh -su: ./test1.sh: Permission denied [email protected]:~/shell# chmod +x ./test1.sh [email protected]:~/shell# ./test1.sh hello 2102 [email protected]:~/shell# ./test1.sh hello 2103 [email protected]:~/shell# ./test1.sh hello 2104 [email protected]:~/shell# sh test1.sh hello 2106
In simple words,
sh file1 executing sh command/executable with file1 as a parameter. In this case file1 doesn't require execute privilege as sh executable read and intercept the commands in the file.
./file1 its nothing but running/executing an executable file file1, hence it requires executable privileges. In this case it executes on the shell mentioned in the shebang
#!/bin/sh if its not mentioned then its on the current shell.
Hoping the above statements are not chaos :)