Fish Shell – Run Command Only If Previous Command Was Successful

fish

Using Bash I've often done things like cd /study && ls -la
I understand that the double ampersand is telling the terminal don't execute part two of this command unless part one completes without errors.

My question is, Having just moved to the Fish shell and trying the same command I get an error stating I can't use && and instructing me to use a single & which I believe backgrounds the task which isn't what I want.

Can anyone tell me the correct syntax to run my old Bash command in the Fish shell?

Best Answer

Instead of &&, which doesn't exist in fish, use ; and the command and:

cd /study; and ls -la

According to the fish tutorial:

Unlike other shells, fish does not have special syntax like && or || to combine commands. Instead it has commands and, or, and not.

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Bash – command substitution handling in fish vs. other shells (sh, bash, zsh)

Ok, I think I have a clue what is going on.

The behaviour you are observing in zsh and bash when executing echo $(mc) is caused by mc.

When you run mc normally, it doesn't react when Ctrl+c is pressed, since it ignores SIGINT. The way to end mc is by pressing F10 and Enter.

When you run echo $(mc) the input goes to the mc process, so it is no wonder that when you press Ctrl+c nothing will happen, because mc ignores SIGINT. But when you run echo $(mc) and press F10 and Enter it will react. (When I then press F10 and Enter again it actually quits; it should quit at the first try but I have no idea why it does not.)

From this fact I deduce that Midnight Commander is running normally, but the output from it is put into the shell buffer, so it can later be used by echo. Something we should consider normal.

Also you think that bash and zsh are hanging, but I would say that they are not hanging but waiting for the echo command to return. But echo can only return when mc returns, which it only does when F10 and Enter are pressed. With this we can also explain what happens when you press Ctrl+z. By pressing the combination mc goes to sleep like it would if you had run mc normally and echo is still waiting for the sleeping mc.

So everything is normal behavior. Except for what fish does. fish seems to start commands run with echo ($command) in the background. It kind of makes sense, since such a command normally does not need any input. For the why and how I have no answer. But you can see that it runs in the background when you enter

echo (mc)
jobs

Bash – How to create a GUI application launcher for xfce4-terminal with fish but inheriting the environment variables from bash

When bash is run as a non-interactive shell it will not source the .bashrc file and if you use a graphical display manager then the login shell used to run the GUI launcher commands might not have sourced the .profile file. Thus, commands run using the GUI launcher might not have the desired environment variables set when run.

A workaround I found was to tell the terminal emulator to run bash in interactive mode (with the -i flag) and then immediately run fish inside of it:

xfce4-terminal -e 'bash -i -c fish'

Best Answer

Related Solutions

Bash – command substitution handling in fish vs. other shells (sh, bash, zsh)

Bash – How to create a GUI application launcher for xfce4-terminal with fish but inheriting the environment variables from bash

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