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[solved] why does "diff" always return "1"?!?
DiTBho:
bash script
--- Code: ---function check_result()
{
local ans="$?" # get the exit status from a terminated program
local answ
if [ "$ans" == "0" ] # 0=success, 1=failure
then
answ="success"
else
answ="failure (ans=$ans)"
fi
echo "$answ"
}
echo "AAAA" > A
cp A B
echo "BBBB" >> B
diff -Naur A B
check_result
# -N, --new-file: treat absent files as empty
diff -Naur A C # C doesn't exist
check_result
--- End code ---
--- Code: ------ A 2021-09-25 13:52:21.012000000 -0000
+++ B 2021-09-25 13:52:21.012000000 -0000
@@ -1 +1,2 @@
AAAA
+BBBB
failure (ans=1)
failure (ans=1)
--- A 2021-09-25 13:52:21.012000000 -0000
+++ C 1970-01-01 00:00:00.000000000 -0000
@@ -1 +0,0 @@
-AAAA
failure (ans=1)
failure (ans=1)
--- End code ---
--- Code: ---NAME
GNU diff - compare files line by line
SYNOPSIS
diff [OPTION]... FILES
DESCRIPTION
Compare FILES line by line.
Mandatory arguments to long options are mandatory for short options too.
--normal
output a normal diff (the default)
-q, --brief
report only when files differ
-s, --report-identical-files
report when two files are the same
-c, -C NUM, --context[=NUM]
output NUM (default 3) lines of copied context
-u, -U NUM, --unified[=NUM]
output NUM (default 3) lines of unified context
-e, --ed
output an ed script
-n, --rcs
output an RCS format diff
-y, --side-by-side
output in two columns
-W, --width=NUM
--left-column
output only the left column of common lines
--suppress-common-lines
do not output common lines
-p, --show-c-function
show which C function each change is in
-F, --show-function-line=RE
show the most recent line matching RE
--label LABEL
use LABEL instead of file name and timestamp (can be repeated)
-t, --expand-tabs
expand tabs to spaces in output
-T, --initial-tab
make tabs line up by prepending a tab
--tabsize=NUM
tab stops every NUM (default 8) print columns
--suppress-blank-empty
suppress space or tab before empty output lines
-l, --paginate
pass output through 'pr' to paginate it
-r, --recursive
recursively compare any subdirectories found
--no-dereference
don't follow symbolic links
-N, --new-file
treat absent files as empty
--unidirectional-new-file
treat absent first files as empty
--ignore-file-name-case
ignore case when comparing file names
--no-ignore-file-name-case
consider case when comparing file names
-x, --exclude=PAT
exclude files that match PAT
-X, --exclude-from=FILE
exclude files that match any pattern in FILE
-S, --starting-file=FILE
start with FILE when comparing directories
--from-file=FILE1
compare FILE1 to all operands; FILE1 can be a directory
--to-file=FILE2
compare all operands to FILE2; FILE2 can be a directory
-i, --ignore-case
ignore case differences in file contents
-E, --ignore-tab-expansion
ignore changes due to tab expansion
-Z, --ignore-trailing-space
ignore white space at line end
-b, --ignore-space-change
ignore changes in the amount of white space
-w, --ignore-all-space
ignore all white space
-B, --ignore-blank-lines
ignore changes where lines are all blank
-I, --ignore-matching-lines=RE
ignore changes where all lines match RE
-a, --text
treat all files as text
--strip-trailing-cr
strip trailing carriage return on input
-D, --ifdef=NAME
output merged file with '#ifdef NAME' diffs
--GTYPE-group-format=GFMT
format GTYPE input groups with GFMT
--line-format=LFMT
format all input lines with LFMT
--LTYPE-line-format=LFMT
format LTYPE input lines with LFMT
These format options provide fine-grained control over the output
of diff, generalizing -D/--ifdef.
LTYPE is 'old', 'new', or 'unchanged'.
GTYPE is LTYPE or 'changed'.
GFMT (only) may contain:
%< lines from FILE1
%> lines from FILE2
%= lines common to FILE1 and FILE2
%[-][WIDTH][.[PREC]]{doxX}LETTER
printf-style spec for LETTER
LETTERs are as follows for new group, lower case for old group:
F first line number
L last line number
N number of lines = L-F+1
E F-1
M L+1
%(A=B?T:E)
if A equals B then T else E
LFMT (only) may contain:
%L contents of line
%l contents of line, excluding any trailing newline
%[-][WIDTH][.[PREC]]{doxX}n
printf-style spec for input line number
Both GFMT and LFMT may contain:
%% %
%c'C' the single character C
%c'\OOO'
the character with octal code OOO
C the character C (other characters represent themselves)
-d, --minimal
try hard to find a smaller set of changes
--horizon-lines=NUM
keep NUM lines of the common prefix and suffix
--speed-large-files
assume large files and many scattered small changes
--color[=WHEN]
colorize the output; WHEN can be 'never', 'always', or 'auto' (the default)
--palette=PALETTE
the colors to use when --color is active; PALETTE is a colon-separated list of terminfo capabilities
--help display this help and exit
-v, --version
output version information and exit
FILES are 'FILE1 FILE2' or 'DIR1 DIR2' or 'DIR FILE' or 'FILE DIR'. If --from-file or --to-file is given,
there are no restrictions on FILE(s). If a FILE is '-', read standard input. Exit status is 0 if inputs are
the same, 1 if different, 2 if trouble.
--- End code ---
I am working on a bash-script, and I am confused by the exit status of the tool "diff", because it always return "1", which should mean FAILURE and others programs return "0" to say "success".
So why does it always return "1" ?!? :-//
magic:
Maybe read TFM that you posted above? :P
retiredfeline:
I haven't looked at your commands but you are doing this the complicated way.
--- Code: ---if diff [options] A B
then
echo "No differences"
else
echo "Differences"
fi
--- End code ---
thinkfat:
diff behaves exactly as described in the man page your posted above.
PKTKS:
not on my shells ???
0 = match
1 = mismatch
2 = error
Paul
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