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Cygwin, Part Three

Cygwin utilities let you do what Windows programs don’t.

View Part 1 of this series here and Part 2 here

The January 2004 Power Tools column Cross-Platform Command Lines presented ways to use the Linux- like features of Microsoft’s shell CMD. However, that shell still requires some thought; you can’t just type a Linux command and expect it to work just as it would in, say, bash.

Windows command-line utilities like FIND.EXE have evolved since the days of DOS, and some of them are quite handy. Of course, Windows also comes with graphical utilities like Windows Explorer, and there are thousands of third-party graphical tools for Windows that enhance the experience and increase the utility of the desktop. Yet in a lot of cases, those Windows applications can’t match the power of the time-tested (and time-improved) GNU shells and utilities.

The Cygwin package (http://www.cygwin.com/) is a Linux-like environment for Microsoft Windows that includes those standard shells and utilities. In this third (and last) article of a series about Cygwin, let’s look at some of the things that can be a struggle with standard Windows tools, but are easy to do with Cygwin utilities. We’ll also see how to use Cygwin scripts and utilities from Windows shortcuts and menus.

Running Shell Scripts From Outside Cygwin

Because the Linux shells have many more features than the Windows CMD interpreter, you may want to run shell scripts instead of Windows batch files.

To run a shell script from outside of a Cygwin shell — such as a Start Menu shortcut file or a CMD prompt — you’ll need to locate the shell executable, pass arguments to it, and possibly set the starting directory. If you make a Windows shortcut that points to the script, Windows runs the application in a text window by default. You can also set window properties like the font, window size, and the length of the command buffer. All of those help you see the results and scroll back to read all of the script’s output. When the application exits, the window will close.

Listing One shows a bash script named watchload. It’s designed to be run from the Cygwin user’s home directory, where a configuration file named .watchload-hosts holds a list of remote hosts to monitor with the Cygwin uptime utility. The script has an endless while loop that uses the bash builtin command read to pause 60 seconds (–t 60) for the user to type a single character (–n 1). If the user doesn’t type q or Q or if read times out, the while loop repeats. (The script is a bit contrived, albeit to demonstrate things about running a script from a Windows shortcut file.)

Listing One: The watchload script

#!/bin/bash
# watchload – run uptime(1) on remote hosts
# Run from $HOME — which has $hosts file
PATH=/cygdrive/c/cygwin/bin
hosts=$(cat .watchload-hosts)
while :
do
date
for host in $hosts; do
ssh $host uptime
done
echo -n “To quit, type q: “
read -t 60 -n 1

case “$REPLY” in
[qQ]) exit ;;
*) echo -e ‘\n’ ;;
esac
done

Figure One shows the shortcut properties dialog, as well as a window with the script running inside. The shortcut target is the Windows-style pathname (using backslashes) of the bash shell; the shell’s argument is a Cygwin-style pathname (using forward slashes) to the script file. The different slash styles are needed because Windows locates the Cygwin shell through a Windows pathname, but the shell expects to see a POSIX- style pathname argument. To make the script run from the current user’s home directory, the “Start in:” field points to the Windows path of that folder. The dialog also sets the icon to a magnifying glass.

Figure One: The watchload shortcut properties and window

You can do the same thing from a CMD prompt by typing the following commands:

C:\> cd \cygwin\home\jpeek
C:\cygwin\home\jpeek> \cygwin\bin\bash bin/watchload

Sending Files to a Script

For some users, an advantage of a window-based environment like Windows is that choices are listed on a menu somewhere. A Cygwin shell prompt, on the other hand, forces the user to know what they’re doing and how to do it.

As you just saw, a good compromise is writing shell scripts that can be run from a Windows shortcut file. You can also install shell scripts and utilities on the Windows “Send to” context menu. (If you haven’t seen this menu, point to an icon, click the right mouse button, and choose “Send to.”) The “Send to” menu lets you right-click on an desktop icon or file (s) in Windows Explorer, then “send” the file to an application.

Windows XP allows “Send to” entries for individual users, as well as a global “Send to” list that’s given to all users. To add an entry to either menu, simply make a shortcut file in the proper Send to folder.

Figure Two: The Windows XP “Send to” menu

Figure Two shows a partly-customized “Send to” menu. The entry for less is a shortcut pointing to C:\cygwin\bin\less.exe; it’s handy for viewing random files. (Look for details on less in this column within the next few months.) The exiftags and identify shortcuts point to little batch files and shell script files that run a utility, then pause until the user presses a key.

For example, here’s the sendto_identify.bat Windows batch file. The %1 passes a single parameter to the identify utility:

"C:\Program Files\ImageMagick-6.2.7-Q8\identify" –verbose %1
pause

What do those “sent” parameters contain? Under what environment do these applications run? A shell script named whatset.sh shows you. Add a shortcut to bash.exe whatset.sh on a “Send to” menu. Then select one or more icons and “send them” to the script. Figure Three demonstrates sending two files to whatset.sh. Listing Two shows the whatset.sh script. It’s just a series of commands, like printenv and set, wrapped in curly-braces so all of the command outputs can be piped to the same less process.

Figure Three: “Sending” two files to whatset.sh

Once you’ve viewed all of the output, press q to quit less and close the” whatset” window.

Listing Two: The whatset.sh script

#!/bin/sh
# whatset – show environment, command line arguments, etc.
# Usage: whatset

bin=/bin # Executables in Cygwin space (Windows PATH may not
include it)

# Collect all outputs, pipe them to ‘less’ with a special prompt:
{
echo “Command line arguments:”
for arg
do echo “‘$arg’”
done

echo “
Environment:”
$bin/printenv

echo “
Bash shell settings (‘set’ command): “
set
} | $bin/less -P’(less) Type f to go forward, b to go back, q to quit: ‘

Flexible File Searching

The Windows XP Search tool is integrated into Windows Explorer, and it has access to the Indexing Service for fast searches. However, the Search tool has a limited number of search parameters, and it’s tough to use the list of files it finds unless you want to point and click on each match.

The Cygwin find (1) and locate (1) utilities are much more flexible. (Read more about find in the September 2002 “Power Tools” column “A Valuable find”, available online at http://www.linux-mag.com/2002-09/power_01.html.) You can build the database for locate from the Cygwin cron facility.

An easy way to save the output of a utility for later re-use is by storing it in a shell variable. Here are examples for bash and tcsh:

$ files=`find /c ... -print`
% set files = `find /c ... -print`

If you want to pass the output of find (or locate) directly to another utility, remember that spaces in Windows filenames can cause trouble. It’s better to use find –print0 and xargs –0. But shell variables generally can’t store the NUL characters output by find –print0. In that case, use a temporary file instead:

find /c ... -print0 > /tmp/find.out
xargs -0 command < /tmp/find.out

Searching Inside Files

The Windows Search tool can look for text strings in files, and the findstr utility has more sophisticated pattern matching. Both of those tools have limited choices for choosing the files you search. The Cygwin shells do a better job, with tools like find that give you lots of control:

$ find /c ... -print0 | xargs grep "..."

Cygwin’s egrep utility lets you choose multiple (and very sophisticated) search patterns. You can also search all of the files in a directory with one grep, then pass the matched filenames to another (possibly different) grep:

$ grep -lZ "..." * | xargs -0 grep "..."

The grep option –l (lowercase “L”) outputs only the matching filenames instead of the matching lines. The –Z (uppercase “Z”) option uses NUL bytes to avoid problems with the spaces in many Windows filenames.

Copying and Moving Files

When you copy or move lots of files with Windows Explorer, the long operation can quit in the middle due to some error, leaving you wondering what went wrong and how to recover from it. The list of objects being moved or copied is shown one-by-one, so it can be tough to figure out what was done and what’s left to do.

Cygwin’s GNU cp and mv utilities have many more options, give you much more control, and have explicit error messages that make recovery easier. For instance, in one window you can run a command to do the copying, saving its verbose output in a log file:

$ cp -vrp * /c/bkup > /d/tmp/cp.log 2>&1

In another window you can watch the log file grow:

$ tail -f /d/tmp/cp.log
`aprog.exe' -> `/c/bkup/aprog.exe'
cp: failed to preserve ownership for
    `/c/bkup/aprog.exe': Permission denied
`bprog.exe' -> `/c/bkup/bprog.exe'
…

Cygwin brings Windows the level of tracking and control that you expect from a Linux system.

Excluding Files From ls

Last month’s column mentioned the bash variable GLOBIGNORE. It lets you choose file types you don’t want shell wildcards to match. GNU ls has its own options to control which files are listed. For instance, the options –B and ––ignore-backups won’t list Emacs backup files. The options –I pattern (uppercase” I”) and ––ignore= pattern won’t list entries matching pattern.

Here’s a handy alias:

alias myls="ls -I '*.[oO][Bb][Jj]' -I '*.[Ll][Oo][Gg]'"

The argument to –I is case-sensitive, so the square brackets allow extensions like .obj and .OBJ. Using the name myls instead of ls means you won’t miss some files as you look around your system with ls. If the list from ls is cluttered, you can use myls instead.

Cygwin-Specific Utilities

Last month’s column mentioned the cygpath utility that lists the locations of the Windows folders like the Desktop, translates Windows pathnames to POSIX/Cygwin equivalents, and more. Cygwin comes with other handy utilities like this. They’re listed at http://cygwin.com/cygwin-ug-net/using-utils.html. One pair of utilities worth mentioning specially is ps and kill.

You can terminate a Windows window and all of the Cygwin processes running inside it, from the standard Windows Task Manager (which you open by typing Ctrl-Alt-Delete under Windows XP). Cygwin comes with a utility named kill that can terminate a single Cygwin process. There’s also a utility named ps to list Cygwin processes. To end a Cygwin process, pass its PID number as an argument to kill.

Many Cygwin programs can be stopped (suspended) just as you would on a Linux system. Simply press Ctrl-Z while the process is the foreground (active) process. Get a list of jobs by typing jobs, and resume a job with fg. Stopping jobs lets you do a lot without opening multiple windows. For instance, you can keep several man pages available, just at the place you finished reading them before, and quickly pull up the one you want.

The Usual Linux Techniques

Of course, there’s more to learn about Cygwin. If you look at a good introduction to Linux, you’ll find that most of those techniques will work under Windows once you’ve installed Cygwin..

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