When I first entered Linux, I used the csh version of the script. In the process of trying, I suddenly found that the instructions written according to the syntax of csh could not run, for example (1.sh):
set a = 100
echo $a
Then the command to run is sh 1.sh, the output is empty, I always thought it was a grammar problem, and then I searched for a long time on the Internet, and finally tried
which ch; the output is /bin/sh, suddenly realized that sh uses bash syntax to execute, so
Under normal circumstances (default), sh uses the syntax of bash, and csh uses the syntax of cshell.