Искусство программирования на языке сценариев командной оболочки




Программирование на языке сценариев командной оболочки - стр. 327


# Here document used as a comment block. : <<DigestFilesDoc

The key (no pun intended) to a Unified Content File System (UCFS) is to distinguish the files in the system based on their content. Distinguishing files by their name is just, so, 20th Century.

The content is distinguished by computing a checksum of that content. This version uses the md5sum program to generate a 128 bit checksum representative of the file's contents. There is a chance that two files having different content might generate the same checksum using md5sum (or any checksum). Should that become a problem, then the use of md5sum can be replace by a cyrptographic signature. But until then...

The md5sum program is documented as outputting three fields (and it does), but when read it appears as two fields (array elements). This is caused by the lack of whitespace between the second and third field. So this function gropes the md5sum output and returns: [0] 32 character checksum in hexidecimal (UCFS filename) [1] Single character: ' ' text file, '*' binary file [2] Filesystem (20th Century Style) name Note: That name may be the character '-' indicating STDIN read.

DigestFilesDoc

DigestFile() { local if=0 # Default, variable name local -a T1 T2

case "$#" in 3) case "$1" in -if) if=1 ; shift ;; * ) return 1 ;; esac ;; 2) : ;; # Poor man's "continue" *) return 1 ;; esac

case $if in 0) eval T1=\( \"\$\{$1\[@\]\}\" \) T2=( $(echo ${T1[@]} | md5sum -) ) ;; 1) T2=( $(md5sum $1) ) ;; esac

case ${#T2[@]} in 0) return 1 ;; 1) return 1 ;; 2) case ${T2[1]:0:1} in # SanScrit-2.0.5 \*) T2[${#T2[@]}]=${T2[1]:1} T2[1]=\* ;; *) T2[${#T2[@]}]=${T2[1]} T2[1]=" " ;; esac ;; 3) : ;; # Assume it worked *) return 1 ;; esac

local -i len=${#T2[0]} if [ $len -ne 32 ] ; then return 1 ; fi eval $2=\( \"\$\{T2\[@\]\}\" \) }

# # # # # Locate File # # # # # # # LocateFile [-l] FileName Location-Array-Name # or # LocateFile [-l] -of FileName Location-Array-FileName # # # # #




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