The majority of shell scripts use a shebang line (#!) at the beginning to control the type of shell used to run the script; this bang line calls for an sh-incantation of bash:
A shebang line (it is short for "sharp" and "bang", two names for # and !) tells the Linux kernel that a specific command (a shell, or in the case of other scripts, perhaps awk or Perl) is to be used to interpret the contents of the file. Using a shebang line is common practice for all shell scripting. For example, if you write a shell script using bash, but want the script to execute as if run by the Bourne shell, sh, the first line of your script will contain #!/bin/sh, which is a link to the bash shell. Running bash as sh will cause bash to act as a Bourne shell. This is the reason for the symbolic link sh, which points to bash.
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