Question

Exercise 7-1. Write a program that converts upper case to lower or lower case to upper, depending on the name it is invoked with, as found in argv[0].

For those of you interested in writing the program, you can find sample solutions here: http://users.powernet.co.uk/eton/kandr2/krx701.html

My question, however, is exactly how do you invoke the program? argv[0] refers to the name of the program, but along with the program’s filepath in addition. When I do a printf() on argv[0], it outputs the full path from /home if I run the program via my code::blocks IDE. If I try to execute the program via the command line with ‘./upper’ (without quotes), argv[0] includes the ‘./’ before the program name.

Is there anyway to invoke this program WITHOUT adding the program path to the PATH environment variable?

Answer 1

You can compile it once, whatever the output filename (e.g.: my_c_program) and with bash, use:

$ exec -a upper ./my_c_program
foo
FOO

$ exec -a lower ./my_c_program
BAR
bar

If you want it to run in a separate shell:

$ bash -c "exec -a upper ./my_c_program"

Basically, the syntax is exec -a <newname> <command>, where <newname> will be argv[0].