I use the watch command to see the contents of my directory changing as a script runs on it (via watch ls dir/)
It's a great tool, except that I can't seem to scroll down or up to see all of the contents once the number of entries fills the vertical length of the screen.
Is there a way to do this?
watch is great, but this is one of the things it can't do. You can use tail to show the latest entries:
watch "ls -rtx dir/ | tail -n $(($LINES - 2))" 
$(($LINES - 2))" to get the latest entries? watch itself. $LINES is an automatic variable that Bash and other shells use to contain the number of lines that the screen can display. You could tail any number you want. tail the last command: { command1 && command2 && command3; } | tail - don't forget the spaces (after the opening and before closing brace) and semicolon after the last command. Remember, the whole chain will be executed each time watch reruns it. I've created a small program that does exactly what you want in python. Find it here, it's called pwatch.
You could use watchall python package; its usage is the same as watch.
sudo pip install watchall 
pwatch, it looks like it supports -d for diffing like watch can. It also binds PgUp/PgDn, it also supports custom intervals. -d option, so you can monitor only some parts of the output. I've created a bash ** swatch ** program that does exactly what you want in bash. In the gif video, you can see how to scroll through a changing mmio file.
#!/bin/bash # # watch a file and scroll # # keys => arrow-up/down, page-up/down, pos1, end # # usages: # swatch -n <timeout_watch> <file> # swatch <file> # # version: 1.1 # dependencies: awk , tput , clear, read # published: https://unix.stackexchange.com/questions/3842/how-can-i-scroll-within-the-output-of-my-watch-command # gif recording: peek , https://github.com/phw/peek # # ============================================= # KEYCODES # ============================================= # https://unix.stackexchange.com/questions/294908/read-special-keys-in-bash # showkey -a # ============================================= # DEFAULTS # ============================================= fname="" line_show_begin=1 line_show_begin_last=-1 console_lines_correction=4 timeout_watch=2 timeout_read=.1 # ============================================= # DEFINE Escape-Sequences # ============================================= # http://ascii-table.com/ansi-escape-sequences-vt-100.php ESC_clr_line='\033[K' ESC_reset_screen='\033c' ESC_clr_screen='\033[2J' ESC_cursor_pos='\033[0;0f' ESC_cursor_home='\033[H' # ============================================= # FUNCTIONS # ============================================= function fn_help() { cat << EOF Usage: ./$0 [-n <timeout>] [<file>] , timeout >0.1s , default 2s EOF } function get_options() { [[ "$1" == "" ]] && { fn_help ; exit 1 ; } while [ -n "$1" ]; do case "$1" in -h|--help) fn_help ;; -n) [[ "$2" == "" ]] && { echo "Error: option -n required <timeout>" ; exit 1 ; } if [[ "$(echo "$2<0.1"|bc)" == "0" ]] ; then timeout_watch="$2" shift else echo "Error: timeout <0.1 not allowed" exit 1 fi ;; -*) echo "Error: unknown option »$1«" exit 1 ;; *) if [[ -f "$1" ]] ; then fname=$1 else echo "Error: file not found »$1«" exit 1 fi ;; esac shift done [[ "$fname" == "" ]] && { echo "Error: file required" ; exit 1 ; } } function fn_print_headline() { hdl_txt_right="${HOSTNAME}: $(date "+%Y-%m-%d %H:%M:%S")" hdl_txt_left="$fname , ${timeout_watch}s , $line_show_begin" hdl_txt_left_length=${#hdl_txt_left} printf '%s%*s\n\n' "$hdl_txt_left" "$(($console_columns-$hdl_txt_left_length))" "$hdl_txt_right" } function fn_print_file() { # --------------------------------------------------- # file lenght can change while watch # --------------------------------------------------- lines_fname=$(awk 'END {print NR}' $fname) line_last=$(($lines_fname-$console_lines)) (( "$line_last" < "1" )) && { line_last=1; clear; } (( "$line_show_begin" > "$line_last" )) && { line_show_begin=$line_last; clear; } # --------------------------------------------------- # print postion changed # --------------------------------------------------- if (( "$line_show_begin" != "$line_show_begin_last" )) ; then line_show_begin_last=$line_show_begin; clear else printf $ESC_cursor_home fi # --------------------------------------------------- # print file section # --------------------------------------------------- fn_print_headline awk -v var1="$line_show_begin" -v var2="$console_lines" 'NR>=var1 {if (NR>var1+var2) {exit 0} else {printf "%s\n",$0 } }' $fname } function fn_console_size_change() { console_columns=$(tput cols) console_lines=$(($(tput lines)-$console_lines_correction)) line_show_begin_last=-1 } function fn_quit() { echo "quit" $0 , $? setterm -cursor on ; exit 0 } # ============================================= # GET OPTIONS # ============================================= get_options "$@" # pass all arguments with double-quotes # ============================================= # INIT TRAP # ============================================= trap "fn_console_size_change" SIGWINCH # https://en.wikipedia.org/wiki/Signal_(IPC)#SIGWINCH trap "fn_quit" INT TERM EXIT # ============================================= # MAIN # ============================================= fn_console_size_change setterm -cursor off while true ; do fn_print_file read -rsn1 -t $timeout_watch k # char 1 case "$k" in [[:graph:]]) # Normal input handling ;; $'\x09') # TAB # Routine for selecting current item ;; $'\x7f') # Back-Space # Routine for back-space ;; $'\x01') # Ctrl+A # Routine for ctrl+a ;; $'\x1b') # ESC read -rsn1 k # char 2 [[ "$k" == "" ]] && return Esc-Key [[ "$k" == "[" ]] && read -rsn1 -t $timeout_read k # char 3 [[ "$k" == "O" ]] && read -rsn1 -t $timeout_read k # char 3 case "$k" in A) # Arrow-Up-Key (( "$line_show_begin" > "1" )) && line_show_begin=$(($line_show_begin-1)) ;; B) # Arrow-Down-Key (( "$line_show_begin" < "$line_last" )) && line_show_begin=$(($line_show_begin+1)) ;; H) # Pos1-Key line_show_begin=1 ;; F) # End-Key line_show_begin=$line_last ;; 5) # PgUp-Key read -rsn1 -t $timeout_read k # char 4 if [[ "$k" == "~" ]] && (( "$line_show_begin" > "$(($console_lines/2))" )) ; then line_show_begin=$(($line_show_begin-$console_lines/2)) else line_show_begin=1 fi ;; 6) # PgDown-Key read -rsn1 -t $timeout_read k # char 4 if [[ "$k" == "~" ]] && (( "$line_show_begin" < "$(($line_last-$console_lines/2))" )) ; then line_show_begin=$(($line_show_begin+$console_lines/2)) else line_show_begin=$line_last fi ;; esac read -rsn4 -t $timeout_read # Try to flush out other sequences ... ;; esac done You can use viddy.
It's a binary that has the basic features of original watch command, including color output and diff highlight, but allows scroll and has a couple more cool features including text search and time machine mode, which allows one go back to the previous versions of the output.
The current one-liner to install it is
wget -O viddy.tar.gz https://github.com/sachaos/viddy/releases/download/v0.3.6/viddy_0.3.6_Linux_x86_64.tar.gz && tar xvf viddy.tar.gz && sudo mv viddy /usr/local/bin And then you can use it like, for example
viddy -d -n 1 ls dir/ to list the dir every second and to highlight the changes. While viddy is running, press ? to get the keyboard shortcuts.
viddy cmd options:
$ viddy -h Usage: viddy [options] command Options: -b, --bell ring terminal bell changes between updates -d, --differences highlight changes between updates -n, --interval <interval> seconds to wait between updates (default "2s") -p, --precise attempt run command in precise intervals -c, --clockwork run command in precise intervals forcibly -t, --no-title turn off header --shell shell (default "sh") --shell-options additional shell options --unfold unfold command result --pty run on pty (experimental, not for Windows) I edited the above script to work with command line
#!/bin/bash # # watch a file and scroll # # keys => arrow-up/down, page-up/down, pos1, end # # usages: # swatch -n <timeout_watch> <file> # swatch <file> # # version: 1.1 # dependencies: awk , tput , clear, read # published: https://unix.stackexchange.com/questions/3842/how-can-i-scroll-within-the-output-of-my-watch-command # gif recording: peek , https://github.com/phw/peek # # ============================================= # KEYCODES # ============================================= # https://unix.stackexchange.com/questions/294908/read-special-keys-in-bash # showkey -a # ============================================= # DEFAULTS # ============================================= command="" TMPFILE=$(mktemp) line_show_begin=1 line_show_begin_last=-1 console_lines_correction=4 timeout_watch=5 timeout_read=.1 # ============================================= # DEFINE Escape-Sequences # ============================================= # http://ascii-table.com/ansi-escape-sequences-vt-100.php ESC_clr_line='\033[K' ESC_reset_screen='\033c' ESC_clr_screen='\033[2J' ESC_cursor_pos='\033[0;0f' ESC_cursor_home='\033[H' # ============================================= # FUNCTIONS # ============================================= function fn_help() { cat << EOF Usage: ./$0 [-n <timeout>] [<command>] , timeout >0.1s , default 5s EOF } function get_options() { [[ "$1" == "" ]] && { fn_help ; exit 1 ; } while [ -n "$1" ]; do case "$1" in -h|--help) fn_help ;; -n) [[ "$2" == "" ]] && { echo "Error: option -n required <timeout>" ; exit 1 ; } if [[ "$(echo "$2<0.1"|bc)" == "0" ]] ; then timeout_watch="$2" shift else echo "Error: timeout <0.1 not allowed" exit 1 fi ;; -*) echo "Error: unknown option »$1«" exit 1 ;; *) #if [[ -f "$1" ]] ; then command=$1 #else # echo "Error: file not found »$1«" # exit 1 #fi ;; esac shift done [[ "$command" == "" ]] && { echo "Error: command required" ; exit 1 ; } } function fn_print_headline() { hdl_txt_right="${HOSTNAME}: $(date "+%Y-%m-%d %H:%M:%S")" hdl_txt_left="$command , ${timeout_watch}s , $line_show_begin" hdl_txt_left_length=${#hdl_txt_left} printf '%s%*s\n\n' "$hdl_txt_left" "$(($console_columns-$hdl_txt_left_length))" "$hdl_txt_right" } function fn_print_file() { # --------------------------------------------------- # file lenght can change while watch # --------------------------------------------------- eval $command > $TMPFILE lines_command=$(awk 'END {print NR}' $TMPFILE) line_last=$(($lines_command-$console_lines)) (( "$line_last" < "1" )) && { line_last=1; clear; } (( "$line_show_begin" > "$line_last" )) && { line_show_begin=$line_last; clear; } # --------------------------------------------------- # print postion changed # --------------------------------------------------- if (( "$line_show_begin" != "$line_show_begin_last" )) ; then line_show_begin_last=$line_show_begin; clear else printf $ESC_cursor_home fi # --------------------------------------------------- # print file section # --------------------------------------------------- fn_print_headline eval $command > $TMPFILE awk -v var1="$line_show_begin" -v var2="$console_lines" 'NR>=var1 {if (NR>var1+var2) {exit 0} else {printf "%s\n",$0 } }' $TMPFILE } function fn_console_size_change() { console_columns=$(tput cols) console_lines=$(($(tput lines)-$console_lines_correction)) line_show_begin_last=-1 } function fn_quit() { echo "quit" $0 , $? setterm -cursor on ; exit 0 } # ============================================= # GET OPTIONS # ============================================= get_options "$@" # pass all arguments with double-quotes # ============================================= # INIT TRAP # ============================================= trap "fn_console_size_change" SIGWINCH # https://en.wikipedia.org/wiki/Signal_(IPC)#SIGWINCH trap "fn_quit" INT TERM EXIT # ============================================= # MAIN # ============================================= fn_console_size_change setterm -cursor off while true ; do fn_print_file read -rsn1 -t $timeout_watch k # char 1 case "$k" in [[:graph:]]) # Normal input handling ;; $'\x09') # TAB # Routine for selecting current item ;; $'\x7f') # Back-Space # Routine for back-space ;; $'\x01') # Ctrl+A # Routine for ctrl+a ;; $'\x1b') # ESC read -rsn1 k # char 2 [[ "$k" == "" ]] && return Esc-Key [[ "$k" == "[" ]] && read -rsn1 -t $timeout_read k # char 3 [[ "$k" == "O" ]] && read -rsn1 -t $timeout_read k # char 3 case "$k" in A) # Arrow-Up-Key (( "$line_show_begin" > "1" )) && line_show_begin=$(($line_show_begin-1)) ;; B) # Arrow-Down-Key (( "$line_show_begin" < "$line_last" )) && line_show_begin=$(($line_show_begin+1)) ;; H) # Pos1-Key line_show_begin=1 ;; F) # End-Key line_show_begin=$line_last ;; 5) # PgUp-Key read -rsn1 -t $timeout_read k # char 4 if [[ "$k" == "~" ]] && (( "$line_show_begin" > "$(($console_lines/2))" )) ; then line_show_begin=$(($line_show_begin-$console_lines/2)) else line_show_begin=1 fi ;; 6) # PgDown-Key read -rsn1 -t $timeout_read k # char 4 if [[ "$k" == "~" ]] && (( "$line_show_begin" < "$(($line_last-$console_lines/2))" )) ; then line_show_begin=$(($line_show_begin+$console_lines/2)) else line_show_begin=$line_last fi ;; esac read -rsn4 -t $timeout_read # Try to flush out other sequences ... ;; esac done nano ~/bin/cwatch.sh chmod +x ~/bin/cwatch.sh alias cwatch="~/bin/cwatch.sh" now you can try it:
cwatch 'ps aux | grep -v grep' 
screencommand withwatchmycommand, I use a bash loop:while : ; do mycommand; sleep 2; doneinstead ofwatch mycommand.