mirror of https://github.com/tLDP/LDP
44 lines
857 B
Bash
44 lines
857 B
Bash
#!/bin/bash
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# param-sub.sh
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# Whether a variable has been declared
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#+ affects triggering of the default option
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#+ even if the variable is null.
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username0=
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echo "username0 has been declared, but is set to null."
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echo "username0 = ${username0-`whoami`}"
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# Will not echo.
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echo
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echo username1 has not been declared.
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echo "username1 = ${username1-`whoami`}"
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# Will echo.
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username2=
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echo "username2 has been declared, but is set to null."
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echo "username2 = ${username2:-`whoami`}"
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# ^
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# Will echo because of :- rather than just - in condition test.
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# Compare to first instance, above.
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#
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# Once again:
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variable=
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# variable has been declared, but is set to null.
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echo "${variable-0}" # (no output)
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echo "${variable:-1}" # 1
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# ^
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unset variable
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echo "${variable-2}" # 2
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echo "${variable:-3}" # 3
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exit 0
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