Advanced bash-scripting guide by Mendel Cooper

By Mendel Cooper

This rfile is either an academic and a reference on shell scripting with Bash. It assumes no earlier wisdom of scripting or programming, yet progresses speedily towards an intermediate/advanced point of guide. The workouts and heavily-commented examples invite energetic reader participation. nonetheless, it's a paintings in growth. The purpose is so as to add a lot supplementary fabric in destiny updates to this record, because it evolves right into a entire booklet that fits or surpasses any of the shell scripting manuals in print.

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Normally, each separate line constitutes a different command, but an escape at the end of a line escapes the newline character, and the command sequence continues on to the next line. (cd /source/directory && tar cf − . ) | \ (cd /dest/directory && tar xpvf −) # Repeating Alan Cox's directory tree copy command, # but split into two lines for increased legibility. # As an alternative: tar cf − −C /source/directory | tar xpvf − −C /dest/directory # See note below. ) If a script line ends with a |, a pipe character, then a \, an escape, is not strictly necessary.

Chapter 6. Quoting 36 Chapter 7. Tests Every reasonably complete programming language can test for a condition, then act according to the result of the test. Bash has the test command, various bracket and parenthesis operators, and the if/then construct. 1. Test Constructs • An if/then construct tests whether the exit status of a list of commands is 0 (since 0 means "success" by UNIX convention), and if so, executes one or more commands. • There exists a dedicated command called [ (left bracket special character).

3" # Error. 3") echo "b = $b" # b=1 Use bc in scripts that that need floating point calculations or math library functions. bitwise operators. The bitwise operators seldom make an appearance in shell scripts. Their chief use seems to be manipulating and testing values read from ports or sockets. "Bit flipping" is more relevant to compiled languages, such as C and C++, which run fast enough to permit its use on the fly. bitwise operators << Chapter 8. Operations and Related Topics 54 Advanced Bash−Scripting Guide bitwise left shift (multiplies by 2 for each shift position) <<= "left−shift−equal" let "var <<= 2" results in var left−shifted 2 bits (multiplied by 4) >> bitwise right shift (divides by 2 for each shift position) >>= "right−shift−equal" (inverse of <<=) & bitwise and &= "bitwise and−equal" | bitwise OR |= "bitwise OR−equal" ~ bitwise negate !

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