simulate diff output using tcl exec diff on two strings

问题

I am trying to produce same output of diff command in tclsh using tcl exec diff on two strings.

Could you please let me know how to solve this example using tclsh exec diff

Working with Bash

$ diff <(echo "Testword") <(echo "Testword2")
1c1
< Testword
---
> Testword2

Failed on TCL

set str1 "Testword"
set str2 "Testword2"

First attempt

% exec diff <(echo "$string1") <(echo "$string2")
extra characters after close-quote

Second attempt

% exec diff <(echo \"$string1\") <(echo \"$string2\")
couldn't read file "(echo": no such file or directory

Third attempt

% exec diff \<(echo \"$string1\") \<(echo \"$string2\")
couldn't read file "(echo": no such file or directory

Fourth attempt

% set command [concat /usr/bin/diff <(echo \\"$string1\\") <(echo \\"$string2\\")]
/usr/bin/diff <(echo \"Malli\") <(echo \"Malli1\")
% exec $command
couldn't execute "/usr/bin/diff <(echo \"Malli\") <(echo \"Malli1\")": no such file or directory.

回答1:

This is a little tricky because you are relying on a bash feature - converting <(some string) to something that looks like a file - but Tcl's exec does not invoke bash or do this conversion by itself. You can make it work by explicitly calling bash from Tcl:

% exec bash -c "diff <(echo '$string1') <(echo '$string2') || /bin/true"
1c1
< Testword
---
> Testword2
%

Note that

The nested quoted here works because single-quote ' is special to bash but not to Tcl
Adding || /bin/true is a hack to force a zero (success) exit code - without this you get an error message "child process exited abnormally" because diff returns a non-zero exit status when its inputs differ. `

来源：https://stackoverflow.com/questions/35838497/simulate-diff-output-using-tcl-exec-diff-on-two-strings

标签

string

tcl

exec

diff

tclsh