Why 'cat' can't read content of pdf files?

command-line pdf cat file-format

6,893

Solution 1

If you call cat on a file containing a text in Chinese¹, it won't print out an English translation. With computer formats, it's the same thing: if you call cat on a file containing data in a certain format, it won't translate it to another format such as plain text. That's not its job: its job is to copy its input to its output without modifying it.

A PDF file isn't a text file. A PDF file can contain text, along with formatting instructions, images, hyperlinks, etc. If you want to read the text in a PDF file, you need to use a tool that understands the PDF file format.

There are a few some recognizable bits in the PDF file: NimbusRomNo9L suggests that the text is written in a Nimbus Roman font. This isn't one of the few fonts that all PDF viewers and printers must have, so it had to be embedded in the PDF file. The text itself (abc) isn't buried in the output because it's compressed.

A common tool to view files regardless of what format they're in is xdg-open. On Debian and derivatives, see is an alternative. Both work by guessing the file format from the extension of the file name and calling an appropriate application. If you want to explicitly extract the text parts (and forget about other information such as images, fonts, the location of the text on the page, etc.), you can call a program to convert the PDF file into text, such as pdftotext.

¹ _{If you understand Chinese, substitue Georgian, or Kanada, or Cree, or whatever language you don't speak.}

Solution 2

It is because pdf is not plain text. cat can only print the file as-is. To see the contents of a pdf file using the command line, you can use pdftotext.

pdftotext pdffile -

Solution 3

cat(1) doesn't "print" files, it is a tool to take a sequence of input files and concatenate them into an output.

What cat file by itself does is to take the contents of file and output it to the terminal. If the file contains text, the terminal will show it as such. PDF files aren't text, and (like any non-text) show as gibberish. Each file type needs some specific program to render it intelligibly.

Today printers often take PDF input to render on the page, or the tools used to print translate into whatever the printer takes automatically.

Solution 4

You can use pdfgrep.

pdfgrep . file.pdf

View more solutions

6,893

Mr. Orange

Updated on September 18, 2022

Comments

Mr. Orange over 1 year

When tried the command cat < 1.pdf it printed a very large output, which was totally incomprehensible to me. The content of 1.pdf was abc.

The output was like this:

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¦åÊmBíöÖ¡÷ÄïÝM{Í1¹@;ÄqÄú             t]È7DJ   Êûc0£jÜÖã\0O8À±(2)èJR'Ø÷=~ÝÆÂµ¡´ oÇKÈ]¹ÞÜY)ÚwÒ?[4ò©Ió¦>G)î¾J&d}ýíÜÅÓò~Ø0 $´Në¿´Èc®pVqí+ëCppG¾ùóßeõõ6GÌ,öfú8Ô7»S[¢S50cq/_9¹jó¿·Ü%×tQSßî▒LðbkÂÒxâ£Ö▒üVAûÇamÏ·Â×«H´+ÆWíç´upèó`I]± ÎëÚwiòtçúwAhO¼²´'Æ©ëÀ0lô?¿ÌIò▒ìXË<»ÅUepçæå¥
SïÒFÒ½Ï·º®Ën.Z×´\£ÁEH@®2ÊçC¢n½¡hÑâ>º´¢YÚXEfg    sôë¥*|zº7>ù!IÂ©Åÿ«;        ;&==
)dS/),÷È´:ÞõH:CÉÑÀiTÌw!u@Âp2÷AÒfµòÜtFIZ^iÿà£ùÖ5ÐsDiërÿ$0b6Ëü~xÏ·._ÏÒõÜr²`wYù;¤²å»äE3óù²ëvÇ»Ó'ãµ~?ÿîMZÍPkh{aÙ1y&tüÙòÕMoó¬²<ñ/ÇÖa?üÊ¯uÝÓjû,¨Üå@/GMa-èGkD}¤ð©fZbYÑlt/      ±Øj¦èRhCå1âÆñ±S@ÖòÁ~e}
>NÀ^²Jà-Û[Mø¡FËB7ÉVy0|ôÉÏjx[ÙÁnneê)wã+ök'R6"dÞqît¿ý,ß¢]MöV>»Ñ@ÞwM0®èçã^F`çFÕ²æL((¬±S¢ÅïÂy§púÓË5y1pÆ{uxëÈOþ'¾7+Öº!í
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              ïþ¨è|Âý6\ U+á¬®[®eVéüvíÜ{ÈL+]¬)ùxþecäæº°ÿoö?,Ä:¯Oò9T:1G4qÞ.ÌtÉÑëEæáHÔ×¬¡ª                                                                                         çc^
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E▒ªpÇ !}¡1{¹_ZlÈë¡Á;u§·+ú,fo ä-AÏ[HM¥×▒ÌÝåìtò*9¼Â^Ñ§▒aÛ`B>/Cö0Þ÷ðiNËþÊ âÄCH´/9fVÎÉó6!vóÑ@ ðÉ!w±y;¯m$i¾äµH+·]YA|åÀD!j{øEÙ^äFÖÑ4▒ääû5þµ)Ãå*y´¹Q« 7í?NýÍ'^õ(*C4f;3ûûn³i|nIï0uo>#n³yµ¹5§*É»&Gtê;c.9 0 objéðÜ}zÔ22T`¦E'ýX®WÈô»&Â>9=ay$àÊGWdwÂ!f·¹eMvÖ=EÞß¢¯ò^¢n`ZÜöQ!Yß§µã gÚEbØù»ÑñÓ                                                             1ªAäØÿPâ'4RÅU]xý'¬¡Â>¹æîtê3Yêy.·¬4ÖçæÍÕOß®×ñh¶ap(<</Type/Font/Subtype/Type1/BaseFont/NimbusRomNo9L-Regu                   9îî~ýÚK°ÓÑ*ÈTt÷ ØL
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500 500 333 389 278 500 500 722 500 500 444 480 200 480 541 0
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0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0/NimbusRomNo9L-Regu
0 333 500 500 167 500 500 500 500 180 444 500 333 333 556 556
0 500 500 500 250 0 453 350 333 444 444 500 1000 1000 0 444
0 333 333 333 333 333 333 333 333 0 333 333 0 333 333 333
1000 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
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Why can't `cat' read content of pdf files?

Sparhawk about 8 years

Because it's a pdf, not plain text? cat is for plain text, e.g. outputting to a terminal emulator. How would you expect cat to output a pdf that contained images and formatting, etc.?
Angel Todorov about 8 years

@harmattan, here's a hint: ls -l -- what's the file size of that pdf file?
user253751 almost 7 years

It can. That is the content of the PDF file.
phuclv about 3 years

catting a binary file like that may produce worse results since there may be some byte sequences in the file that match the ANSI sequences and changes the terminal behavior completely