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<div><a href="index.html" title="">Macaulay2Doc</a> > <a href="___The_sp__Macaulay2_splanguage.html" title="">The Macaulay2 language</a> > <a href="_reading_spfiles.html" title="">reading files</a></div>
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<div><h1>reading files</h1>
<div>Sometimes a file will contain a single expression whose value you wish to have access to. For example, it might be a polynomial produced by another program. The function <a href="_get.html" title="get the contents of a file">get</a> can be used to obtain the entire contents of a file as a single string. We illustrate this here with a file whose name is <tt>expression</tt>.<p/>
First we create the file by writing the desired text to it.<table class="examples"><tr><td><pre>i1 : fn = temporaryFileName()
o1 = /tmp/M2-13413-1</pre>
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<tr><td><pre>i2 : fn << "z^6+3*x*z^4+6*y*z^4+3*x^2*z^2+12*x*y*z^2+12*y^2*z^2+x^3+6*x^2*y+12*x*y^2+8*y^3" << endl << close
o2 = /tmp/M2-13413-1
o2 : File</pre>
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Now we get the contents of the file, as a single string.<table class="examples"><tr><td><pre>i3 : get fn
o3 = z^6+3*x*z^4+6*y*z^4+3*x^2*z^2+12*x*y*z^2+12*y^2*z^2+x^3+6*x^2*y+12*x*y^2
+8*y^3</pre>
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This isn't quite what you want, because a string containing a description of a polynomial is not the same as a polynomial. We may use <a href="_value.html" title="evaluate">value</a> to evaluate the string and produce the corresponding polynomial, after first setting up a polynomial ring to contain it.<table class="examples"><tr><td><pre>i4 : R = ZZ/101[x,y,z]
o4 = R
o4 : PolynomialRing</pre>
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<tr><td><pre>i5 : f = value get fn
6 4 4 2 2 2 2 2 3 2 2
o5 = z + 3x*z + 6y*z + 3x z + 12x*y*z + 12y z + x + 6x y + 12x*y +
------------------------------------------------------------------------
3
8y
o5 : R</pre>
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<tr><td><pre>i6 : factor f
2 3
o6 = (z + x + 2y)
o6 : Expression of class Product</pre>
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Often a file will contain code written in the Macaulay2 language. Let's create such a file.<table class="examples"><tr><td><pre>i7 : fn << "sample = 2^100
print sample
" << close
o7 = /tmp/M2-13413-1
o7 : File</pre>
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Now verify that it contains the desired text with <a href="_get.html" title="get the contents of a file">get</a>.<table class="examples"><tr><td><pre>i8 : get fn
o8 = sample = 2^100
print sample</pre>
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To load and execute that code, use <a href="_load.html" title="read Macaulay2 commands">load</a>. This is the function you will use most often for using bits of code you have previously written, unless you have incorporated them into a package, in which case you would use <a href="_load__Package.html" title="load a package">loadPackage</a>.<table class="examples"><tr><td><pre>i9 : load fn
1267650600228229401496703205376</pre>
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The command <a href="_needs.html" title="read Macaulay2 commands if necessary">needs</a> can be used to load a file only if it hasn't already been loaded.<table class="examples"><tr><td><pre>i10 : needs fn</pre>
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For debugging or display purposes, it is sometimes useful to be able to simulate entering the lines of a file one by one, so they appear on the screen along with prompts and output lines. We use <a href="_input.html" title="read Macaulay2 commands and echo">input</a> for this.<table class="examples"><tr><td><pre>i11 : input fn</pre>
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There are other ways to manipulate the contents of a file with multiple lines. First, let's use <a href="_peek.html" title="examine contents of an object">peek</a> to observe the extent of this string returned by <a href="_get.html" title="get the contents of a file">get</a>.<table class="examples"><tr><td><pre>ii12 : sample = 2^100
oo12 = 1267650600228229401496703205376</pre>
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The resulting string has newlines in it; we can use <a href="_lines.html" title="split a string into lines">lines</a> to break it apart into a list of strings, with one row in each string.<table class="examples"><tr><td><pre>ii13 : print sample
1267650600228229401496703205376</pre>
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We may use <a href="_peek.html" title="examine contents of an object">peek</a> to observe the extent of these strings.<table class="examples"><tr><td><pre>ii14 : </pre>
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We could even use <a href="_stack.html" title="join nets or string vertically">stack</a> to assemble the lines of the file into a net.<table class="examples"><tr><td><pre>i15 : peek get fn
o15 = "sample = 2^100
print sample
"</pre>
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Now let's remove that file.<table class="examples"><tr><td><pre>i16 : lines get fn
o16 = {sample = 2^100, print sample}
o16 : List</pre>
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