The diff command reveals differences between two files, if any. Sometimes commands need LC_ALL=C prepending them on the command line.
Give the sftp command the login/server info. Use -p for preserving the dates and permissions for any files transferred, and -r for recursively copying directories. Use a colon to delimit the login/server from the optional path, which defaults to the home directory of the account.
sftp -pr account@domain.tld:/some/path
Similarly, in emacs the dired command can be evoked with a colon-delimited remote path, t.i. a protocol, a login/server, and a path.
...or even with ssh:
The default protocol is evoked with "-", which usually resolves to scp. (Actually, it references the variable tramp-default-method, and that method is usually named "scp", which itself uses scp.) The default login/server is the current login/server, and the default path is the home directory for the given login/server. Therefore, "/-::" implies these defaults of "/scp:account@computer.local:~", for whatever the current account and computer name happens to be.
For example, Controlx d will evoke dired (directory edit) by prompting in the minibuffer for the path of a directory. Or, within dired use Shiftc for copying a file, and it asks for the destination path. Simply type a remote path and the marked files will be copied to the remote destination, even with ssh.
List disks and partitions with lsblk -p, mount a disk with mount, unmount a disk with umount, and always sync before disconnecting a disk.
find and grepFind all html files then grep for "Text". The "{}" is replaced by find with each filename; or "{} +" to use as many filenames as possible for the command executed (for possibly greater efficiency).
find . -name "*.html" -exec grep -l "Text" {} +
For file name searches only (f.e. for all HTML files, including ".htm": -name '*.htm*'), the emacs command ESC x find-name-dired prompts for a directory for recursively searching and then a shell wildcard pattern (case-insensitive, without quotes), which returns a dired listing of results. Then use % g to mark all files whose contents contain a match for a regular expression.
dired
Within dired the command ESC x dired-do-find-regexp (shortcut: Shifta) will search marked files or recursively search a marked directory for a regexp matching file contents.
Within dired the command ESC x dired-do-isearch-regexp (shortcut: ESC s a ESC Controls) will interactively search file contents of marked files.
The ‑crop option will crop multiple times within an image when the geometry is only the size without a position ("#x#", rather than "#x#+#+#"). Saving to a TIFF results in multiple images within it.
Exporting all images from a TIFF can be done with the percent format "%d" in the output name, along with the -scene option for the starting number.
Using ‑repage is generally a good idea when cropping or rotating.
The ‑virtual‑pixel option is needed for affecting the color of pixels for rotations other than 90° increments, and its default method value is edge. The ‑virtual‑pixel method black, as in:
Compression is specified with -compress followed by type: None, BZip, Fax, Group4, JPEG, JPEG2000, Lossless, LZW, RLE or Zip. List all types with:
magick -list compress
The "Lossless" type is for JPEG, when available. The ICO format uses PNG compression by specifying "Zip", t.i. -compress ZIP.
Compression for JPG for line drawings has seemed pretty much unnoticeable at 50% (‑quality 50), and minor blurring noticeable at 25% when zoomed. However, 20% compression seems okay and also the lowest acceptable, which has resulted in approximately 1% of the TIFF size. At 15% compression there has been large swaths of color noticeable.
Identify the current dimensions, the resolution depth and units, and the compression type and quality.
identify -format "%wx%h, %xx%y %U, %C %Q" image.tif
Identify the original dimensions (before resizing), image depth, and image colorspace.
identify -format "%G, %[bit-depth], %[colorspace]" image.tif
Identify the list of any embedded profiles (or a warning).
identify -format "%[profiles]" image.tif
dired's ! shortcut in emacs
Mark some files within dired and then type ! to evoke a shell command on them. Within the shell command use the "?" character for one file at a time, and the "*" character for all files at once.
mogrify +distort SRT 90 +repage ?
convert ? -set filename:f '%t' -gravity South -crop "100%x54%+0+0" +repage '%[filename:f]-2.jpg'
convert ? -set filename:f '%t' -resize "240x240>" -density 72 '%[filename:f]_240px.jpg'
convert ? -set filename:f '%t' +write '%[filename:f].jpg' -resize "240x240>" -density 72 '%[filename:f]_240px.jpg'
convert ? -set filename:f '%t' -resize "2560x2560>" -density 72 +write '%[filename:f]_2560px.jpg' -resize "240x240>" -density 72 '%[filename:f]_240px.jpg'
convert ? -set filename:f '%t' -quality 20 '%[filename:f].jpg'
convert * name-of-document.pdf
Size a 600 DPI image into a multiple of 50 for width and height (for scaling simply to 72 DPI in PDFs later), by first making the dimensions an even number. Also annotate the four corners with label indicating the side of paper, f.e. Front, Inside, or Back.
magick ? -set filename:f '%t' -background "#000" -splice "%[fx:w%2]x%[fx:h%2]" +repage -gravity Center -crop "%[fx:50*(trunc(w/50)-2)]x%[fx:50*(trunc(h/50)-2)]+0+0" +repage -bordercolor "#000" -border 150 -gravity NorthWest -font "Verdana" -pointsize 100 -fill "#FFF" -annotate +25+20 'Front' -annotate "90x90+%[fx:w-40]+25" 'Front' -annotate "180x180+%[fx:w-25]+%[fx:h-20]" 'Front' -annotate "270x270+40+%[fx:h-25]" 'Front' -quality 20 '%[filename:f].jpg'
magick ? -set filename:f '%t' -background "#000" -splice "%[fx:w%2]x%[fx:h%2]" +repage -gravity Center -crop "%[fx:50*(trunc(w/50)-2)]x%[fx:50*(trunc(h/50)-2)]+0+0" +repage -resize "200x200>" -density 72 -bordercolor "#000" -border 20 -gravity NorthWest -font "Verdana" -pointsize 16 -fill "#FFF" -annotate +20+2 'Front' -annotate "90x90+%[fx:w-4]+20" 'Front' -annotate "180x180+%[fx:w-20]+%[fx:h-2]" 'Front' -annotate "270x270+4+%[fx:h-20]" 'Front' -quality 20 '%[filename:f]_240px.jpg'
Use a shell when a TIFF has multiple images inside it to reference its first image.
convert image.tif[0] -set filename:f '%t' +write '%[filename:f].jpg' -resize "240x240>" -density 72 '%[filename:f]_240px.jpg'
convert *.tiff[0] +distort SRT 90 +repage -set filename:f '%t' +write '%[filename:f].jpg' -resize "240x240>" -density 72 '%[filename:f]_240px.jpg'
Errors along the lines of "cache resources exhausted" probably indicate the "/etc/ImageMagick-[version number]/policy.xml" has been changed, perhaps when upgraded. Check the resources with:
magick -list resource
Typically, the policy has had nothing set at all, so simply comment out anything in that file in order to use the defaults (of nothing set at all).
View a directory of files named with numbers within dired with Controlx d (command: ESC x dired), hide details with the shortcut ( (command: ESC x dired-hide-details-mode) to show only filenames, and then use Controlx Controlq (command: ESC x dired-toggle-read-only) to switch to write mode. A message appears saying how to save changes (Controlc Controlc), or cancel (Controlc ESC).
format to convert the number back to regular text. For example, add 1 to matched numbers:
format"%d"(+ \#& 1))
The \, is for using lisp for the replacement; see 15.10.2 Regexp Replacement. Within that, the \#& conveniently converts the whole match to a number (when possible). The same prefix "\#" works for parenthesized matches like \#1 and so on. Also, multi-digit parenthesized references are possible when using lisp with a replacement, t.i. beyond 1–9. For example, \27 for the 27th parenthesized match, or the numerical value of the match with \#27.
After all desired editing is done, use Controlc Controlc to save the changes to the filenames, and then read-only mode will be enabled again.
insert(format"%d"(*(/ 5400 50)6)))
insert(format"%d"(-(mark)(point))))
shell-command (shortcut: ESC !) will insert the results of a shell command at point in the current buffer when used with the universal argument (Controlu). For example, to insert the width of an image into the buffer using identify from ImageMagick:
identify -format "%w" image.jpg