Fails to understand %, \%, and \\

[andersk]

From crontab(5) (cron 3.0pl1-124.1ubuntu1):

The  ``sixth'' field (the rest of the line) specifies the command to be
run.  The entire command portion of the line, up  to  a  newline  or  %
character, will be executed by /bin/sh or by the shell specified in the
SHELL variable of the crontab file.  Percent-signs (%) in the  command,
unless escaped with backslash (\), will be changed into newline charac‐
ters, and all data after the first % will be sent  to  the  command  as
standard  input.  There  is  no way to split a single command line onto
multiple lines, like the shell's trailing "\".

Although this is not specifically documented, the source indicates that a backslash can also be used to escape another backslash (but not any other character, except after the first %).

[pbyrne]

Interesting. I've never run into that before. If I'm properly reading properly, I should be treating % and \ in the command like so:

• foo%bar will perform foo and send bar to STDIN
• foo % bar will perform foo and send bar to STDIN (preserving whitespace)
• foo%bar%baz will perform foo and send bar\nbaz to STDIN
• foo \% bar will perform foo % bar
• foo \\ bar will perform foo \ bar

@andersk, care to correct me if I'm misunderstanding? Also, thanks for this bug report!

[danielmotaleite]

@pbyrne that is correct

the % is a trap for many people when using cron, specially in things like date +%Y%m%d , that will fail and people don't understand why