CODEWITHSUNDEEP
linuxbashshell
Radu Rădeanu
Radu Rădeanu

Reputation: 2732

Strange behavior using a space in front of $SHELL environment variable in bash

When I use the following command, everything works as expected (a new gnome-terminal is open, the current working directory is changed and the terminal remains open):

gnome-terminal -e "bash -c 'cd /';$SHELL"
#                                ↑
#                      no space character here

But when I use:

gnome-terminal -e "bash -c 'cd /'; $SHELL"
#                                 ↑
#                           note the space

I can see a terminal that opens, but I can't see if the current working directory is changed or not because the terminal it closes immediately.

My question is: why this is happening; how can be wrong if I put a space in the second case?

Upvotes: 0

Views: 150

Answers (2)

Mark Plotnick
Mark Plotnick

Reputation: 10271

gnome-terminal does its own parsing of the command given to it, using g_shell_parse_argv, which apparently doesn't consider ; to be a word separator, so if a ; is adjacent to a non-whitespace character, it is considered to be part of that non-whitespace character's word.

This can result in surprising behavior if the command you pass to gnome-terminal has shell metacharacters in it.

I used strace on the gnome-terminal process to see what it does. The first command

gnome-terminal -e "bash -c 'cd /';$SHELL"

results in gnome-terminal running the following command

execve("/bin/bash", ["bash", "-c", "cd /;/bin/bash"])

The second command

gnome-terminal -e "bash -c 'cd /'; $SHELL"

results in gnome-terminal running the following command

execve("/bin/bash", ["bash", "-c", "cd /;", "/bin/bash"])

That being said, you should also note that a command such as bash -c 'cd /' will not have a lasting effect on the working directory of any command run after it. So I think that the first command you typed got the desired result only because of the gnome-terminal parsing misfeature, and a more robust way of writing it would be

gnome-terminal -e "bash -c 'cd /;$SHELL'"

Upvotes: 3

that other guy
that other guy

Reputation: 123570

In the first case, gnome-terminal executes 

bash -c "cd /;/bin/bash"

in the second case, it runs

bash -c "cd /;" /bin/bash

The first case means "evaluate cd /;/bin/bash", which will cd and run an interactive shell.

The second case means "evaluate cd /; with $0 set to /bin/bash", which will run cd and then exit.

Upvotes: 6

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