heredoc (docs emblebed) [miguel angel torres egea]

Aquesta pàgina és només de lectura. Podeu veure'n el codi font, però no podeu canviar-la. Consulteu el vostre administrador si penseu que això és degut a algun error.

= heredoc (docs emblebed)

un //heredoc// es la manera de "embutir" un documento de texto dentro de un script para volcar a nuestro criterio.

== ejemplos
el //EOF// usado en los ejemplos no deja de ser una etiqueta, no es mandatory... podríamos usar MITEXTO, la cuestión es definir principio y fin con la misma etiqueta

===sintaxis básica
no se permite indentación?
<code bash>
#!/bin/bash
OUT=/tmp/output.txt
 
cat <<EOF
Status of backup as on $(date)
Backing up files $HOME and /etc/
EOF
 
echo "Starting backup using rsync..."
</code>

=== + indentación natural del doc
permite indentación del documento!
<code bash>
#!/bin/bash
OUT=/tmp/output.txt
 
cat <<-EOF
  Status of backup as on $(date)
  Backing up files $HOME and /etc/
EOF
 
echo "Starting backup using rsync..."
</code>

=== + no bash expansion
<code bash>
#!/bin/bash
OUT=/tmp/output.txt

# No parameter and variable expansion, command substitution, arithmetic expansion, or pathname expansion is performed on word.  
# If any part of word is quoted, the delimiter  is  the  result  of  quote removal  on word, and the lines in the here-document 
# are not expanded. So EOF is quoted as follows
cat <<'EOF' >$OUT
  Status of backup as on $(date)
  Backing up files $HOME and /etc/
EOF
</code>

resultado:
  Status of backup as on $(date)
  Backing up files $HOME and /etc/

===  + redirección (también permite >>)
<code bash>
#!/bin/bash
OUT=/tmp/output.txt
 
cat <<EOF >$OUT
  Status of backup as on $(date)
  Backing up files $HOME and /etc/
EOF
</code>


=== en memoria!
<code bash>
#!/bin/bash
OUT=/tmp/output.txt
 
## in memory here docs 
## thanks https://twitter.com/freebsdfrau
exec 9<<EOF
  Status of backup as on $(date)
  Backing up files $HOME and /etc/
EOF
 
## continue
echo "Starting my script..."
echo "Doing something..."
 
## do it
cat <&9 >$OUT
 
echo "Starting backup using rsync..."
</code>





/via: [[https://www.cyberciti.biz/faq/using-heredoc-rediection-in-bash-shell-script-to-write-to-file/]]