I want to search the program ">>" that is by which you append to a file.
I run the code unsuccessfully in Mac
find . -print0 | xargs -0 grep " >> "
I get too many results to find the correct app.
The program is not among other teletypes at /bin.
How can you find the program ">>"?
There is no program called ">>" - it's just a part of the shell's syntax.
This is a shell operator, not a program at all.
Read the code for bash. Or find a simpler implementation of a Bourne Shell. There must be several on the web. Here is one http://heirloom.sourceforge.net/sh.html.
This is not a program, this is a shell construct. Try man bash.
As others have mentioned, it's just part of the syntax. Like + and - are part of math syntax. If you want to overwrite a file, use a single >, to append use double >>.
It works both ways. So if you want to use a file as input, just use <. Each line of the file will be passed to the command.
command < file.txt
Related
I'm trying to automate my test runner better. For that I need the update file name in a variable. As this name depends on a the version I'm trying to use a find with a pattern to get the file name. That works just fine in bash.
However if I use that same pattern in expect find complains that it can't find anything.
My guess is that expect is doing something to my wildcards. However my experiments with {}, "", '' or \ didn't result in it working.
I guess I could create a helper sh script to write it into a file and then read that file but I don't like that solution and there has to be an option to pass characters with special tcl meaning as arguments.
At the moment my call looks something like this with an absolute path in front of the pattern:
set pattern {[0-9]*/*test*}
set updateFile [exec find ${pattern} -type f]
The result is that find reports '[0-9]*/*test*': No such file or directory. The pattern is what I would expect and when I call find [0-9]*/*test* -type f in bash it results in the expected file path. Find also works fine as long as I don't have any wild cards.
Has anybody an idea what is wrong?
When you run find [0-9]*/*test* -type f in Bash, it's Bash who interprets the wildcard [0-9]*/*test* and expand it to multiple files. And then Bash would pass the expanded multiple files to find. That's to say find never sees the wildcard.
For exec find $pattern -type f, Tcl would not interpret what's in $pattern and pass it directly to find. Unfortunately find also does not interpret the wildcards here so it fails with error like find : '[0-9]*/*test*': No such file or directory.
To work around, you can invoke find with bash -c:
exec bash -c "find $pattern -type f"
I'm confused when i should use awful.spawn and when to use awful.spawn.with_shell. To me these look and work the same.
The only difference I see is that in awful.spawn you can set client rules and make a callback.
I would appreciate any examples or rules on when to use each one.
awful.spawn.with_shell really does not do more than spawning the given command with a shell: https://github.com/awesomeWM/awesome/blob/c539e0e4350a42f813952fc28dd8490f42d934b3/lib/awful/spawn.lua#L370-L371
function spawn.with_shell(cmd)
if cmd and cmd ~= "" then
cmd = { util.shell, "-c", cmd }
return capi.awesome.spawn(cmd, false)
end
end
So, why would one want that? Some things are done by shells. For example, output redirections (echo hi > some_file), command sequences (echo 1; echo 2) or pipes (echo hello | grep ell) are all done by a shell. None of these work when starting a process correctly.
Why would one not want a shell? For example, argument escaping is way more complicated when a shell is involved. When you e.g. want to start print a pipe symbol (no idea why one would need that), then awful.spawn({"echo", "|"}) just works, while with a shell you need to escape the pipe symbol the appropriate number of times. I guess that awful.spawn.with_shell("echo \\\|") would work, but I am not sure and this is the point.
Also, a shell that does nothing is an extra process and is a tiny bit slower than without a shell, but this difference is really unimportant.
I will use ls output for pipe input, so I need to escape the file name. when I use GNU ls, It works well. what's the equivalent in BSD ls? I hoping the output is like this.
$ gls --quoting-style escape t*1
text\ 1 text1
Why are/were you trying to use ls in a pipeline? You should probably be using find (maybe with -print0 and xargs -0, or -exec).
I suppose you could use ls -1f and then run the output through vis (or some similar filter) with some appropriate options to add the necessary quoting or escaping of your choice, but without knowing what you are feeding filenames into, and what (if any) other options you would want to use with ls, it's impossible to give much better guidance.
From the freebsd man page on ls there is no such option, however, you can try -m which will give you a comma separated streamed output:
-m Stream output format; list files across the page, separated by
commas.
I tried it on osx and it gave me:
$ ls -m
Hello World, Hello World.txt, foo.txt
That is a lot easier to parse from a script.
I want to remove lots of temporary PS datasets with dataset name like MYTEST.**, but still can't find an easy way to handle the task.
I meant to use a Shell command below to remove them
cat "//'dataset.list'"| xargs -I '{}' tsocmd "delete '{}'"
However, first I have to save the dataset list into a PS dataset or Unix file. In Unix, we can redirect output of ls command into a text file: "ls MYTEST.* > dslist", but on TSO or ISPF panel, seems no simple command to do that.
Anyone has any clue on this? Your comment would be appreciated.
Rexx ISPF option is probably the easiest and can be used in the future, but options include:
Use the save command in ispf 3.4 to save to a file, then use a rexx program on the file created by the save command
listcat command, in particular
listcat lvl(MYTEST) ofile(ddname)
then write a rexx program to do the actual delete
Alternatively you can use the ISPF services LMDINIT, LMDLISTY & LMDFREE in a rexx program running under ISPF i.e.
/* Rexx ispf program to process datasets */
Address ispexec
"LMDINIT LISTID(lidv) LEVEL(MYTEST)"
"LMDLIST LISTID("lidv") OPTION(list) dataset(dsvar) stats(yes)"
do while rc = 0
/* Delete or whatever */
end
"LMDFREE LISTID("lidv")"
For all these methods you need to fully qualify the first High level qualifier.
Learning what Rexx / ISPF will serve you into the future. In the ISPF Editor, you can use the model command to get Templates / information for all the ISPF commands:
Command ====> Model LMDINIT
will add a template for the lmdinit command. There are templates for rexx, cobol, pl1, ISPF-panels, ISPF-skeletons messages etc.
Thanks Bruce for the comprehensive answer. According to Bruce's tips, I just worked out a one-line Shell command as below:
tsocmd "listcat lvl(MYTEST) " | grep -E "MYTEST(\..+)+" | cut -d' ' -f3 | xargs -I '{}' tsocmd "delete '{}'"
Above command works perfectly.
Update - The IDCAMS DELETE command has had the MASK operand for a while. You use it like:
DELETE 'MYTEST.**' MASK
Documentation for z/OS 2.1 is here.
I'm trying to use the Unix command paste, which is like a column-appending form of cat, and came across a puzzle I've never known how to solve in Unix.
How can you use the outputs of two different programs as the input for another program (without using temporary files)?
Ideally, I'd do this (without using temporary files):
./progA > tmpA;
./progB > tmpB; paste tmpA tmpB
This seems to come up relatively frequently for me, but I can't figure out how to use the output from two different programs (progA and progB) as input to another without using temporary files (tmpA and tmpB).
For commands like paste, simply using paste $(./progA) $(./progB) (in bash notation) won't do the trick, because it can read from files or stdin.
The reason I'm wary of the temporary files is that I don't want to have jobs running in parallel to cause problems by using the same file; ensuring a unique file name is sometimes difficult.
I'm currently using bash, but would be curious to see solutions for any Unix shell.
And most importantly, am I even approaching the problem in the correct way?
Cheers!
You do not need temp files under bash, try this:
paste <(./progA) <(./progB)
See "Process Substitution" in the Bash manual.
Use named pipes (FIFOs) like this:
mkfifo fA
mkfifo fB
progA > fA &
progB > fB &
paste fA fB
rm fA fB
The process substitution for Bash does a similar thing transparently, so use this only if you have a different shell.
Holy moly, I recent found out that in some instances, you can get your process substitution to work if you set the following inside of a bash script (should you need to):
set +o posix
http://www.linuxjournal.com/content/shell-process-redirection
From link:
"Process substitution is not a POSIX compliant feature and so it may have to be enabled via: set +o posix"
I was stuck for many hours, until I had done this. Here's hoping that this additional tidbit will help.
Works in all shells.
{
progA
progB
} | paste