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+====== shell tips ======
+Here's a tutorial: [[http://tldp.org/LDP/abs/html/|Advanced Bash-Scripting Guide]].
+===== Quick Tips =====
+The [[http://www.reddit.com/r/bashtricks/comments/hdfzc/execute_previous_command_as_root/|History Expansion character]] is "!".  To search the history for a previous "scp" command and only print it, try the first line below. But if you want to interactively find that command, type ''<Ctrl>+r,scp''.
+<code bash>
+$ !?scp?:p
+$ ^rscp
+</code>
+===== bash expansion =====
+<code bash>
+$ cp file{,.bk}
+</code>
+expands to
+<code bash>
+$ cp file file.bk
+</code>
+Replace all files that end with .JPG to .jpeg
+<code bash>
+for file in *.JPG; do mv $file ${file%.JPG}.jpeg; done
+for file in *.JPG; do mv $file ${file/JPG/jpeg}; done
+</code>
+Then there are two different "rename" commands:
+<code bash>
+rename .JPG .jpg *.JPG
+rename "s/JPG/jpg/" *.JPG
+</code>
+===== Command Template =====
+Here's a template for shell commands that demonstrates a number of arguments, length of argument, etc.  It could still stand a bit of clean-up according to the [[http://google-styleguide.googlecode.com/svn/trunk/shell.xml|Google Shell Style Guide]].
+Another good resource is [[http://robertmuth.blogspot.com/2012/08/better-bash-scripting-in-15-minutes.html|Better Bash Scripting in 15 minutes]].
+<code bash>
+#!/usr/bin/env bash
+set -eu -o pipefail # See: https://sipb.mit.edu/doc/safe-shell/
+declare -r SCRIPT_NAME=$(basename "$BASH_SOURCE")
+## exit the shell (default status code: 1) after printing the message to stderr
+die() {
+    echo >&2 "$1"
+    exit ${2-1}
+}
+## the options used by this script
+DISK=e
+declare -i VERBOSE=0
+## exit the shell (with status 2) after printing the message
+usage() {
+    echo "\
+$SCRIPT_NAME -hv [Drive Letter] (default: $DISK)
+    -h      Print this help text
+    -v      Enable verbose output
+"
+    exit 2;
+}
+## Process the options
+while getopts "hv" OPTION
+do
+  case $OPTION in
+    h) usage;;
+    v) VERBOSE=1;;
+    \?) usage;;
+  esac
+done
+## Process the arguments
+shift $(($OPTIND - 1))
+if [ $# -eq 0 ]; then
+    : # Let the default be used
+elif [ $# -eq 1 ]; then
+    if [ ${#1} -eq 1 ]; then
+        DISK=$1
+    else
+        # 64 is EX_USAGE from sysexits.h
+        die "$SCRIPT_NAME: Drive Letter can only be one character long." 64
+    fi
+else
+    usage;
+fi
+## Lock this if only one instance can run at a time
+# UNIQUE_BASE=${TMPDIR:-/tmp}/"$SCRIPT_NAME".$$
+LOCK_FILE=${TMPDIR:-/tmp}/"$SCRIPT_NAME"_"$DISK".lock
+if [ -f "$LOCK_FILE" ]; then
+  die "$SCRIPT_NAME is already running. ($LOCK_FILE was found.)"
+fi
+trap "rm -f $LOCK_FILE" EXIT
+touch $LOCK_FILE
+## The main work of this script
+if [ ! -d /cygdrive/"$DISK"/backup/Users ]; then
+    mkdir -p /cygdrive/"$DISK"/backup/Users
+fi
+((VERBOSE==1)) && echo "Starting at $(date)"
+rsync /cygdrive/c/Users/me /cygdrive/"$DISK"/backup/Users
+# We add "|| true" because we don't want to stop
+# if the directory was already empty
+rm -r /cygdrive/c/Users/me/tmp/* || true
+# Note how we find the number of cores to use
+make -C build_subdirectory all -j$(grep -c ^processor /proc/cpuinfo)
+</code>
+===== Miscellaneous Shell Tips =====
+If you want a single column of just the file and path names, you can get it like so:
+<code bash>
+ls --format=single-column
+</code>
+But if you don't know what you're doing, you might construct something like so:
+<code bash>
+ls -Al | tr -s ' ' | cut -d ' ' -f10-
+</code>
+  - List "almost all" items in "long" format (one line per item)
+  - Squeeze repeats of the space character
+  - Cut out everything from before the 10th column and show everything afterwards.
+Of course, if you could assert the following:
+  * none of the first columns were repeats (awk would only identify the first repeated column)
+  * the desired column didn't have delimiters in it (filenames with spaces)
+...you could use awk
+<code bash>
+... | awk '{print $10}'
+</code>
+Anyway, given a list of directories, they can be inserted into a cp command with xargs if you need.
+<code bash>
+cat list_of_directories_at_one_level.txt | xargs -I {} cp -r $SOURCEDIRPREFIX:{} $DEST
+</code>
+Useful bash command for finding strings within python files...
+<code bash>
+find . -name \*.py -type f -print0 | xargs -0 grep -nI "timeit"
+find . -type f \( -name \*.[ch]pp -or -name \*.[ch] \) -print0 | xargs -0 grep -nI printf
+</code>
+Interesting way to use ''grep -v'' to remove paths from a list generated by ''find''.  Not sure about the escaped ''|'' character, though...
+<code bash>
+#!/bin/bash
+find $PWD -regex ".*\.[hcHC]\(pp\|xx\)?" | \
+    grep -v " \|unwantedpath/unwantedpath2\|unwantedpath3" > cscope.files
+cscope -q -b
+</code>
+Here's how to find if a symbol is in a library, and how to search lots of object files and print the filename above the search...
+<code bash>
+nm obj-directory/libmyobject.a | c++filt | grep Initialize_my_obj
+find bindirectory/ -name \*.a -exec nm /dev/null {} \; 2>/dev/null | \
+    c++filt | grep -P "(^bindirectory.*\.a|T Initialize_my_obj)"
+</code>
+Also handy to merge two streams together...
+<code bash>
+( cat file1 && cat file2 ) | sort
+</code>
+When a little quick math is needed, use ''bc''
+<code bash>
+$ bc <<< "obase=16;ibase=10;15"
+F
+$ bc -l <<< 1/3
+.33333333333333333333
+$ bc <<< "scale=2; 1/3"
+.33
+$ bc <<< "obase=10;ibase=16;B"
+</code>
+and, when coverting from hex to dec...
+<code bash>
+echo $((0x2dec))
+</code>
+But, then again, does that really seem easier than,
+<code>
+python -c "print int('B',16)"
+</code>
+There's a bash way to calculate how many days ago a date was:
+<code bash>
+$ echo $(( ($(date +%s) - $(date -d "2012-4-16" +%s)) / 86400 ))
+</code>
+And a Python way...
+<code python>
+python -c "import datetime; print (datetime.date.today() - datetime.date( 2012, 4, 16 )).days"
+</code>
+And for displaying lines clipped at the right edge of the window instead wrapped:
+<code bash>
+cat_one_line_per_row() {
+  cat "$@" | expand | cut -b1-$COLUMNS
+}
+</code>
+or a "clip" command like so:
+<code bash>
+alias clip="expand | cut -b1-\$COLUMNS"
+</code>
+ctags's man page says that one of its bugs is that it has too many options.  Ain't that the truth.  Make note of the obscure flag here, ''--c++-kinds=+p'', that tells ctags to process prototypes and method declarations.
+<code bash>
+ctags -n --if0=yes --c++-kinds=+p --langmap=c++:+.inl.lst \
+    --langmap=asm:+.inc --file-tags=yes -R --extra=fq \
+    --exclude=unwanted_file.lst \
+    --exclude='*unwanted-directory*/*' \
+    --regex-C++='/^.*CINIT.(.+),.*,.*,.*/CURLOPT_\1/'
+</code>
+When you want to repeat a command a few times...
+<code bash>
+seq 1 50 | xargs -I{} -n1 echo '{} Hello World!'
+</code>
+When you've set up Perforce to use an application for diff with ''export P4DIFF='vim -d' '', you can still do a regular diff like so:
+<code bash>
+$ P4DIFF=; p4 diff hello-world.cpp
+</code>
+It's [[http://stackoverflow.com/questions/47007/determining-the-last-changelist-synced-to-in-perforce|hard to be sure which Perforce changelist you sync'ed if you didn't explicitly sync to a changelist]].
+So, use ''p4_sync'' to sync to a specific changelist, and update a source file too.
+<code bash>
+p4_sync() {
+    p4 changes -s submitted -m1 ... | tee p4_sync_to_change.txt
+    changelist=`cut -d " " -f 2 p4_sync_to_change.txt`
+    changelist_filename=changelist.h
+    p4 sync ...@$changelist
+    if [ -w $changelist_filename ]
+    then
+	sed -i 's/"[0-9]\+";/"'$changelist'";/' $changelist_filename
+    fi
+}
+</code>
+Note the use of $@ vs "$*" in the next function that automatically saves an archive of a telnet session. Also note that I remove spaces and colons. (Colons because they screw with opening files directly at line numbers).
+<code bash>
+telnet_log() {
+    curtime=$(date -Iseconds | tr : .)
+    args=$(echo "$*" | tr ' ' '_')
+    telnet $@ | tee $HOME/telnetlog/$args\_${curtime::-5}.log
+}
+last_telnet_log() {
+    ls -d1t $HOME/telnetlog/* | head -n 1
+}
+</code>
+Of course if you do that, you'll want to occasionally (via cronjob?) delete old archives.
+<code>
+find $HOME/telnetlog/ -type f -mtime +6 -delete
+</code>
+Keywords: bash shell sh zsh
+====== .vimrc tips ======
+Here's an alternative way to automatically save backups (with dates in the filename) everytime you save a file.
+<code>
+set backup
+set backupdir=~/.vim/backup/
+au BufWritePre * let &bex = '-' . strftime( "%Y%m%d-%H%M%S" )
+</code>
+That makes a lot of files, so you can clean out the backups with a cron job like this:
+<code>
+# at 3 in the morning on Mondays, delete files older than 30 days
+3 * * 1 find $HOME/.vim/backup/ -type f -mtime +30 -delete
+</code>
+====== expect tips ======
+What to do when it's not sure you're going to make a connection?
+<code>
+set times 0
+set made_connection 0
+set timeout 120
+while { $times < 2 && $made_connection == 0 } {
+    spawn nc $SERVER
+    send "\r"
+    expect {
+        "login:" {
+            send "john.doe\r"
+            set made_connection 1
+        } eof {
+            sleep 1s
+            set times [ expr $times + 1 ]
+        } timeout {
+            puts "Didn't expect to timeout."
+            exit
+        }
+    }
+}
+</code>
+I think the following is wrong-headed. It's not usually the case that spawn will fail.
+<code>
+set times 0;
+while { $times < 2 && $made_connection == 0 } {
+    if { [ catch { spawn nc $SERVER } pid ] } {
+        set times [ expr $times + 1 ];
+        sleep 1s;
+    } else {
+        set made_connection 1
+    }
+}
+</code>
+====== Perl tips ======
+The module ''Search::Dict'' has a "''look''" function that can be used to do a binary search in an ordered dictionary file (a logfile (or log file) that starts with timestamps works). ''File::SortedSeek'' might also be recommended.
+====== Application Memory Usage ======
+Use VM Resident Set Size.  See VmRSS below. (Note the [[http://stackoverflow.com/questions/10400751/how-do-vmrss-and-resident-set-size-match|difference between RSS and VmRSS]]. If one process has memory mapped, it's not usable any any other process)
+<code bash>
+host:# ps -ef | grep etflix
+default   1532  1081  6 22:06 ?        00:01:21 pkg_/metflix
+root      2108  1046  0 22:26 ?        00:00:00 grep etflix
+host:# pidof netflix
+host:# cat /proc/1532/status
+Name:   MAIN
+...
+Groups:
+VmPeak:   220776 kB
+VmSize:   210096 kB
+VmLck:         0 kB
+VmHWM:     95168 kB
+VmRSS:     74488 kB
+...
+</code>
+Or, while running an application, to see how much is free over time, do this from another shell:
+<code bash>
+while [ 1 ]
+do
+    free -m | grep Mem
+    sleep 3
+done
+</code>
+Alternatively, to see the RSS use of that process alone:
+<code bash>
+while true; do sync; cat /proc/$(pidof yourprocess)/status | grep VmRSS; sleep 1; done
+</code>
+====== Measuring Available Memory ======
+This note doesn't entirely make sense to me. Maybe need to study up on "cat /proc/meminfo" vs. "cat /proc/vmstat" vs. "vmstat".
+The best measure I've found for "available memory" is nr_inactive_file_pages+nr_active_file_pages+nr_free_pages from /proc/vmstat. And then you have to subtract out some heuristically determined value which is base system working set. (That heuristically determined value can be 30-40MB.)
+The command ''free'' just isn't a great indicator in general of how much memory is available because it doesn't account for the cached  file-backed pages that could be dumped to make more memory available.
+====== Shared Memory Usage ======
+To increase limit to 256MB from command line:
+<code bash>
+echo "268435456" > /proc/sys/kernel/shmmax
+echo "268435456" > /proc/sys/kernel/shmall
+</code>
+Or, edit /etc/sysctl.conf:
+<code>
+kernel.shmmax= 268435456
+kernel.shmall= 268435456
+</code>
+====== Performance Metrics ======
+  * Use [[http://man7.org/linux/man-pages/man1/perf-timechart.1.html|perf-timechart]]
+  * [[https://github.com/gperftools/gperftools|gperftools]]
+And you can scrape logs that start with timecodes to create Spreadsheet charts. Given logs like:
+<code>
+-10-13 19:54:44  memory 22a4
+</code>
+On a Macintosh:
+<code bash>
+grep memory devicelogs.txt | tr -s ' ' | cut -d " " -f 1,2,4 | \
+sed 's/\([0-9\-]\+\) \([0-9:]\+\).[0-9]\+ \([0-9a-f]\+\)/\1,\2,=DATEVALUE("\1")+TIMEVALUE("\2"),=HEX2DEC("\3")/' >  heapinfo.csv; \
+open heapinfo.csv -a "Microsoft Excel"
+</code>
+And on Linux, instead of opening Microsoft Excel, that last line would be:
+<code bash>
+libreoffice --calc heapinfo.csv
+</code>
+====== Cron ======
+Keep tasks serialized with [[https://linux.die.net/man/1/flock|flock(1)]]:
+    (
+         flock -n 9 || exit 1
+         # ... commands executed under lock ...
+    ) 9>/var/lock/mylockfile
+====== Retrieving Symbols with addr2line ======
+You can gather a backtrace (stacktrace) with this piped command to addr2line.
+    $ cat << EOF | cut -d " " -f 3 | tr -d "[]" | \
+      addr2line -e builds/austin/src/platform/gibbon/netflix | \
+      xargs -d '\n' realpath --relative-to=.
+    > 7/22 app() [0xf7878] (0xf7878)
+    > 8/22 app() [0x39c2f8] (0x39c2f8)
+    > 9/22 app() [0xe1964] (0xe1964)
+    > EOF
+    src/Application.h:106 (discriminator 3)
+    src/platform/main.cpp:521
+    src/Application.cpp:95
+====== Sort by Frequency ======
+I ran the following P4 command to find out who's been editing a file recently:
+   $ find . -name fname.cpp | xargs p4 filelog -s -m 10 | \
+     awk '/^\.\.\. #/ {print $9}' | cut -d @ -f 1 | sort | uniq -c | sort -nr
+====== jq Tips ======
+jq is really handy. Here's a tip for some processing I often do:
+<file javascript fruits.txt>
+{ "fruits":
+  {
+    "apple":
+       {
+          "name": "Apple",
+          "price" : 2
+       },
+    "banana":
+       {
+          "name": "Banana",
+          "price" : 3
+       },
+    "count": 2,
+    "open": true
+  }
+}
+</file>
+<code>
+$ jq '.fruits|del(.count,.open)|with_entries(.value |= .price)' fruits.txt
+{
+  "apple": 2,
+  "banana": 3
+}
+# with_entries(f) is an alias for to_entries | map(x) | from_entries
+jq '.fruits|del(.count,.open)|to_entries|map(.value |= .price)|from_entries' f
+{
+  "apple": 2,
+  "banana": 3
+}
+$ jq '.fruits|del(.count,.open)|[to_entries[]|{(.key): .value.price}]|add' fruits.txt
+{
+  "apple": 2,
+  "banana": 3
+}
+</code>
+<file javascript fruit_ip.txt>
+{
+  "192.168.144.52": {
+    "ipAddress": "192.168.144.52",
+    "attributes": {
+      "model": "apple",
+      "name": "David's apple"
+    }
+  },
+  "192.168.144.40": {
+    "ipAddress": "192.168.144.40",
+    "attributes": {
+      "model": "banana",
+      "name": "David's banana"
+    }
+  }
+}
+</file>
+<code>
+$ jq '[to_entries[]|{"key":.value.attributes.name,"value":.key}]|from_entries' fruit_ip.txt
+{
+  "David's apple": "192.168.144.52",
+  "David's banana": "192.168.144.40"
+}
+$ jq '[.[]|{(.attributes.name):.ipAddress}]|add' fruit_ip.txt
+{
+  "David's apple": "192.168.144.52",
+  "David's banana": "192.168.144.40"
+}
+$ jq -r "to_entries|map(\"\(.value.attributes.name) = \(.key)\")|.[]" fruit_ip.txt
+David's apple = 192.168.144.52
+David's banana = 192.168.144.40
+</code>
+====== Protips for find ======
+[[https://stackoverflow.com/a/2962015/9181|How to use "sh -c" without {} in find's -exec]].
+Given a lib directory, I wanted to find all the actual .so files that needed libz.
+  find lib -type f -name \*.so\* -exec sh -c 'objdump -p "$1" | grep "NEEDED.*libz"' - {} \; -print
+Note that you can pass -print (or -and -print) after a -exec argument. Also, the " - " is just a placeholder for $0 (usually the command name, in this case "sh"), we want $1 to be {}. It outputs results like:
+    NEEDED               libz.so.1
+  lib/libprotoc.so.13.0.2
+====== Additional Keywords ======
+Linux, Unix, *nix